232
A TABLE FOR N A M I N G
A
TABLE
BIVALVE
BIVALVE SHELLS OF T H E
FOR
SHELLS
OF
CRAG.
NAMING THE
CRAG,
WITH A REVISED LIST OF THE SPECIES. BY
CLAUDE M O R L E Y ,
F.E.S.,
F.G.S.,
F.Z.S.
1. T h e sole merit claimed for it is that the T a b l e Covers with equal efficiency any stage of the Shell's growth : hence sizes are rarely indicated, because of use merely in the case of mature specimens that anyone, with slight practice, can name from Searles W o o d ' s descriptions and figures ; b u t he presents no dichotomous T a b l e s of distinctions. I myself have used the present one during the last four busy years in collecting 160 out of the total 226 species occurring in S u f f o l k ; and I find it sufficiently handy as a rough, initial guide before proceedim,' for confirmation to W o o d ' s work, the obfuscating synonym} of which is here fully entered.—NOTE 2. N u m b e r s preceding localities refer to W o o d ' s work.—NOTE 3. Nearly all the Crag localities are in Suffolk, excepting Walton-on-Naze in Essex, Bramerton and Aldeby in Norfolk. T h e Red Crag localities are purposely not in order of t h e various ' h o r i z o n s ' that Geologists have ascribed to different patches, because I find, by pretty t h o r o u g h practical investigation of every patch now exposed, no basis whatsoever for such restrictions : the entire fauna (Protozoa, Porifera, Ccelenterata, Polyzoa, Annelida, Echinodermata, Mollusca, Cirrhipedia with other Crustacea, and Vertebrata) supplies no reliable criterion for such theoretical division, above the mainly-derivative basal nodule-bed.*—NOTE 4. T h e formations are ascendantly abbreviated thus : CC. Coralline Crag; R C . Red Crag ; M C . Mammalian seu Norwich seu Icenian Crag ; CB. Chillesford Bed of clay; L G . , M G . , U G . , and P G . are Lower a n d M i d d l e and U p p e r and Post-Glacial drift.—NOTE 5. Nothing novel is here attempted : for the present, we are trying to widerstand what W o o d knew.—NOTE 6. I need hardly add that the Shell's base is the hinged beak seu u m b o , whence ribs or folds (plicse) or S t r i a e usually radiate to the apex and sides, intersecting
NOTE
*I certainly think there may be such things as horizons on the extreme margins of the old seas ; but also that many of the places we work may be merely the churned-up sea-bottom, which never was a shore in Crag days. Of course, we know the sea has a remarkable way of depositing things according to their weight : shingle is always large high up the beach, an<i smaller as one gets to low-water mark. I fancy Cornelians must be specifically lighter than other pebbles, as they have a tendencv to be washed among shingle smaller than themselves ; Amber may be considered a mere featherweight, and is left among the big shingle as though or no account. T h e association of Shells and Coral, so familiär to Concnologists, is surely only a question of weight.— C. G. DOUGHTV, in !>'• 25 Jan. 1933.