Crag Palaeontology, Pt. 1

322

CEMENT STONE AT NACTON AND SEPTARIA GENERALLY

considerably harder than any calcareous cement stone yet formed in a similar way in Reading Beds. There cannot be many such examples of sheets of rock in the populär sense of the word at or near surface in Suffolk—excluding erratics.

Miss Willis has kindly pointed out to me a short reference to septaria in our Proceedings for 1938, Vol. I, Pt. 1, xxx.

F.

H. A.

ENGLEHEART.

NOTES ON CRAG PALAEONTOLOGY—1

By P.

G.

CAMBRIDGE

SYNOPSIS : The genera Ostrea, Cyprina and Teilina as understood by Searles V. Wood are reviewed and a species new to the Crag, Glibertia prosperi van Meulen, is recorded.

It is now over one hundred years since Searles V. Wood commenced his famous work on the Crag Mollusca and although considerable work has been done on the recent mollusca, involving many alterations to the older and better known names, no comprehensive work on the Plio-Pleistocene shells has been published in this country for many years. The author hopes to be able to review the Crag fauna in a series of articles of which this forms the first.

The term Crag is used loosely in these notes for convenience, in place of the more accurate but clumsy term Plio-Pleistocene, to indicate the related Coralline (Gedgravian) and Red (Ipsvician) Crag. The Norwich Crag (Icenian) is recorded separately.

As a matter of convenience the boundary between the Pliocene and the Pleistocene is placed by most modern writers at the base of the Waltonian. How long a period of time elapsed between the deposition of the Coralline Crag and the Waltonian Red Crag is not known, but certain Continental horizons are missing from the succession in this country. The occasional appearance of worn examples of Angulus benedeni (Nyst), Surculites intorta (Brocchi) etc., in the area of disturbed Crag between Felixstowe and Ipswich would seem to point to the destruction of some Crag beds and the incorporation of the remnants in the Newbournian Crag.

T h e writer has been greatly assisted by Dr. L. R. Cox and Mr. Castell of the British Museum, L. v. d. Slik of Rotterdam, Dr. M. Glibert of Brüssels, and others who have helped with

NOTES ON CRAG PALAEONTOLOGY

323

specialised knowledge. The opinions expressed, except where specifically stated otherwise, are those of the writer and any errors or omissions are solely his.

MOLLUSCA Young oysters are fairly common in the Coralline Crag and become abundant locally, sometimes forming beds as at Ramsholt. Most examples in the Red Crag are worn and rolled, frequently bored by the sponge Cliona. In such a variable genus it is extremely difficult to define the limits of a species and some authors have recognised a number of Crag " species " based on slight variations in form. The writer recognises the following species : Ostrea edulis L. Miocene (Anversian) to Recent. Wood, Crag Mollusca, P1.2, Fig. 1, 2b (as O. princeps juv), PI. 5, Fig. 7 (O. ungulata) and Suppl. PI. 8, Fig. 10 (O. plicatulä).

Well preserved examples in the Coralline Crag ; many worn valves in the Red Crag, a proportion of which are probably derived from the Coralline Crag. I do not know of any oyster beds in the Red Crag with the shells in situ where they lived.

Ostrea princeps Wood. Red Crag, mainly Newbournian.

Wood, Crag Mollusca, PI. 1, Fig. 1, PI. 2, Fig. 2a (non 2b = O. edulis).

In 1938, C. Brakman suggested that this unusual species represented the ideal adult form of the common oyster, referring it to Ostrea edulis var princeps (Wood.). Like Wood, he noted the difficulty of separating the young of this species from O. edulis and suggested that this was because the species were identical.

All the young examples in the Wood Collection (British Museum) are from the Coralline Crag but after examining a number of large collections I have been unable to find an adult example of O. princeps from the Coralline Crag. It is therefore concluded that the juvenile examples recorded from the Coralline Crag are actually Ostrea edulis and that princeps does not occur in that formation.

The specimens from the Red Crag mostly came from the area about Newbourne, Waldringfield, etc., the valves being separated and the imbricated scales more or less worn. The distribution and condition of the specimens both suggest the possibility of the species being derivative. Among the Eocene Ostreidae in the British Museum collections, specimens were found which were indistinguishable from some examples of O. princeps. I suggest that the Crag shell may be Ostrea bellovacina Lamarck. T h e presence of numbers of worn examples of Turritella d.imbricataria in the same area confirms the fact that derived Eocene fossils, other than of London Clay age, occur in the Crag.

324 NOTES ON CRAG PALAEONTOLOGY Until further evidence can be found it seems best to retain Wood's name for the species as represented in hisfiguresPI. 1, Fig. 1 and PI. 2, Fig 2a. The original species was an aggregate and the specimens from the Red Cragfiguredby Wood cannot be traced. Eight specimens from the Wood Collection in the British Museum (L.87556 - 63) agree very closely with his figures and are considered by the writer as typical of Wood's species as emended.

Pycnodonte cochlear (Poli). Miocene (Holland, Germany Belgium, etc.). to Recent (Mediterranean).

Wood, Crag Mollusca, PI. 2, Fig lc (as Ostrea spectrum Leath Common in the Coralline Crag, especialy near Ramsholt.

Examples in the Red Crag are probably derived.

Var. alata Foresti. This is the variety, distinguished by the prolonged processes,figuredby Wood from the Coralline Crag at Ramsholt.

Var. navicularis Brocchi. A somewhat variable form but characterised by the oval contour and very convex left valve.

Common in the Crag.

Var. hennei Nyst. This variety, especialy when worn, shows a remarkable resemblance to Gryphaea arcuata Lmk., of the Lias This distinct form has not been recorded in this country but occurs in the Scheide area and could easily be mistaken for derived examples of the Mesozoic shell.

Var. pedemontana Mayer (=Ostrea acuta Bell M.S.). An elongate variety occasionally found in the Crag.

Pycnodonte vesicularis (Lmk.). Cretaceous ; Derivative in t Red Crag.

A single example from Felixstowe is in the Geological Museum (Number xxiii 3 /35a).

Glibertia prosperi van Meulen. Scaldisien, Holland ; Coralline Crag, Gedgrave.

This minute member of the Condylocardiidae wasfirstfound in glauconitic sand inside a Nassarius reticosus (Sowerby) dredg from shell banks on the bed of the Scheide estuary. Later, further examples were found in shell drift containing many small Plio-Pleistocene fossils, on the beach at Ritthem, Walcheren, Holland. Early this year, while sorting small shells from Gedgrave, the writer discovered a right valve of this species (Author's Coli. No. G2086) which compared exactly with Dutch specimens.

The species was unknown to Wood and has probably been overlooked by later workers on account of its small size. To assist in its future identification a description and sketch of the species is given.

325

NOTES ON CRAG PALAEONTOLOGY

" Small, very tumid, ovate. Exterior and interior glossy.

Prodissoconch smooth, cap-like and very large in comparison with the adult V a l v e s . The hinge consists of several large projecting callosities. Ligament internal in a groove between the teeth. Two adductor muscle scars are generally visible and are situated rather low. The sculpture is concentric but almost obsolete. The shell is integripalliate ; the pallial line is almost invisible."

Length Height Thickness Holotype: Left valve 1.06m.m.

0.94m.m.

0.55m.m.

Paratype: Right valve 1.45m.m.

1.22m.m.

0.42m.m.

F I G . 1.

Fig. 1.

Glibertia prosperi v. d. Meulen

Arctica islandica (L.). Miocene to Recent (Atlantic).

Wood, Crag Mollusca, PI. 18, Fig. 2a - d.

Pygocardia rustica (J. Sowerby). Anversien, Scaldisien, Coralline and Red Crags.

Wood, Crag Mollusca, PI. 18, Fig. la - e.

Common in the Coralline Crag but rare in the Red Crag where it may be derivative. The shape of this species is typically almost round ( = var tumida Wood, PI. 18, Fig. la, c and e).

Var. defranchii van Beneden, 1835. This varietal name has priority oVer var. elongata Wood, 1853 (PI. 18, Fig. lb, d).

The variety is more elongate and more or less rectangular in shape.

Macoma balthica (L.).

Mollusca, PI. 22, Fig. 1.

Icenian

to

Recent.

Wood,

Crag

Although this species has been recorded from the Scaldisien of Belgium (Maillieux, 1933 p. 191), in this country it makes its first appearance in the Icenian where it is especially characteristic

NOTES ON CRAG PALAEONTOLOGY 326 of the Weybournian stage. Previous records of this species from the Red Crag were probably due to mistaking young or distorted examples of M. obliqua for M. balthica and in the absence o actual specimens its presence in the Red Crag is doubtful.

Macoma obliqua (J. Sowerby). Scaldisien, Coralline and Red Crags, Chilesford Clay and Norwich Crag. Wood, Crag Mollusca, PI. 21, Fig. 7a - d.

Very variable in shape. Extremely abundant in the Red Crag and parts of the Norwich Crag. Extremely thick (gerontic ?) examples sometimes occur in the Red Crag.

Macoma calcarea (Gmelin). Pleistocene to Recent (Northern Wood, Crag Mollusca, PI. 21, Fig. 6a - d (as Tellina lata Gm Although this species has been recorded from the Red Crag it is more characteristic of later beds and probably makes its first appearance in the Icenian. The rare Crag examples may be distorted specimens of M. obliqua. Geologists collecting in the Crag should look out for this shell in an attempt to confirm its ränge in time.

Tellina (Moerella) donacina L. Miocene (North Europe Italy) to Recent. Wood, Crag Mollusca, PI. 22, Fig. 3a, b.

Common in the Coralline Crag : rare in the Red Crag, probably due to the fragility of the shell.

Tellina (Fabulina) fabula Gmelin. Pleistocene, Eemien, Rec Wood, Crag Mollusca, PI. 21, Fig. 3.

This species has been recorded from the Icenian of Southwold and the Chilesford Clay.

Tellina (Oudardia) compressus (Brocchi). Miocene to (Mediterranean). Wood, Crag Mollusca, P. 22, Fig. 6a - b (as Tellina donacilla Wood).

Recorded from the Coralline Crag of Sutton. Further examples are required to confirm this identification.

Tellina (Angulus) benedenii Nyst et Westendorp. Dies Scaldisien, and Red Crag. Wood, Crag Mollusca, PI. 21, Fig. 2a-d.

Rare in the Red Crag and mainly occurs in the Newbournian area, where it may be derived from earlier beds. A common shell in the Scaldisien of Belgium.

Tellina (Angulus) squalida Mont. Miocene to Recent. Jeffr Brit. Conchology, Vol. 5, PL xli, Fig. 3.

Although not yet recorded as a fossil in this country this shell has been found in the Miocene of the Continent and therefore may eventually be discovered in the Crag.

NOTES ON CRAG PALAEONTOLOGY

327

Tellina (Angulus) praetenuis Woodward. Scaldisien, Red Crag, Icenian. Wood, Crag Mollusca, PI. 21, Fig. 5a - c.

Common everywhere in the Red Crag.

Arcopagia crassa (Penn). Scaldisien to Recent. Wood, Crag Mollusca, PL 21, Fig. la - d.

Fairly common in the Red Crag and has been recorded from the Coralline Crag. Sometimes thickened and distorted examples occur in the Crag.

Arcopagia balaustina (L.). Coralline Crag to Recent. Wood, Crag Mollusca, PI. 21, Fig. 4.

Coralline Crag of Sutton, not common. The bed where Wood and R. Bell collected their specimens doe's not appear to be exposed at present and I have not found this species there.

BIBLIOGRAPHY Wood, Searles V.

1848-1882

Forbes & Hanley

1853

Jeffreys, J. G .

Winckworth, R. " Basteria "

1863-1869 1932-1934 1938-1956

Glibert, M .

1945

Heering J.

1950

Heering, J.

1950

Monograph of the Crag Mollusca.

M o n . Pal. Soc. L o n d o n .

A History of British Mollusca, London.

British Conchology, 5 Vols.

Articles in the Journal of Conchology.

Various articles, many in D u t c h , by C. Brakman, v. d. Meulen, etc., Rotterdam.

Faune Malacologique de Miocene de la Belgique. I - Pelecypodes Bruxelles. (In French).

Miocene Pelecypoda of the N e t h e r lands. Maastricht. ( I n English).

Pelecypoda (and Scaphopoda) of the Pliocene and Pleistocene of the Netherlands.

Maastricht.

(In English).

BOTANICAL SECTION At a meeting of the Botanical Section in December, 1955, a new Committee was formed. Its primary purpose is the Organisation and compilation of a new Suffolk Flora to bring the work of Hind up to date.

T h e Botanical Society of the British Isles is also engaged on a flora distribution survey of the British Isles, known as the Distribution Maps Scheme and areas are being recorded in 10 Kilometre squares. For this purpose, the D.M. Scheme has issued small printed field cards with a comprehensive list of flora.