~ 
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BIVALVIA. iL 
very abnormal, the length measuring nearly twice the height; these he has called Cr. 
ensiformis, with a mark of doubt against this specific name. I think they are only 
deviations from the more common type, as I can find no other difference than length, and 
almost every intermediate form may be observed. The anal area, or that flat space beyond 
the diagonal ridge, is divided into two unequal parts, produced, I presume, by the division 
or septum of the syphons. 
This species is said by M. Deshayes not to be abundant in the Paris Basin, where it 
does not attain to so large a size. Some of our specimens show a little erosion at the 
umbones, while others are there quite perfect. 
There is another shell of Mr. Edwards’s marked as “ Cr. rostralis ?” which I have also 
had figured (Pl. XXIII, fig. 4 @, 4), but which, I think, is scarcely entitled to specific 
isolation; it is narrow at the siphonal termination; it is, however, said to be always 
smaller and more compressed, with a less curve to the basal margin, and the external 
ridges rather narrower. I propose to call it var. gradata, as rostralis is another species. 
Crassatella sulcata, Sow., is a name given in a list of species from the Nummulitic deposit 
in the Province of Barcelona, by M. Alex. Vézian (‘ Bull. de la Soc. Géol. de France,’ 
2nd ser., vol. xiv, p. 387), but it does not appear to be admitted by M. Deshayes. 
18. CRassaTELLA TENUISULCATA, Hdwards MS. Pl. XXIII, fig. 2 a, 6. 
Spec. Char. C. Testa transversd, elongatd, tumidd, tenui-sulcatd, sulcis numerosis ad 
regionem ani evanentioribus ; valde inequilaterali, crassd ; pedi-regione convexd siphoni- 
regione majore productd, elongatd, margine dorsali depressd, concaviusculd ; umbonibus 
elevatis obtusis ; lunuld depressd ; marginibus crenulatis. 
Shell transverse, elongate, tumid, covered externally with numerous and rather fine 
ridges, except over the anal region or above the diagonal ridge, where it is nearly smooth, 
or with numerous visible lines of growth. Siphonal side the larger, narrow and truncated; 
umbones rather prominent and obtuse ; lunule depressed ; ventral margins crenulated. 
Length, 1sth inch; height, +4ths of an inch. 
Locality. Barton (Hdwards). 
This is not rare, and the two valves are often found united. It differs from C. sulcata 
in the exterior ornament, which is not so coarse, and the siphonal or anal side is more 
produced, and the dorsal margin on that side is depressed. ‘The finer sulci terminate at 
the angle formed by the diagonal ridge. The nearest approach to this species appears to 
be C. donacialis, Desh., but that shell is more equilateral, and it wants the carinated 
edge of this species. Another shell, called /ineatissima, from Bramshaw and Brook (PI. 
XXIV, fig. 6 a, 4), is, I think, a variety of this species. 
