BIVALVIA. 171 



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 (PI. XXIII, fig. 4 a, b), 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. Vezian (' Bull, de la Soc. Geo], de Prance,' 

 2nd ser., vol. xiv, p. 387), but it does not appear to be admitted by M. Deshayes. 



13. Crassatella tenuisulcata, Edioards MS. PI. XXIII, fig. 2 a, b. 



Spec. Char. C. Testa transversa, elongatd, tumidd, tenui-sulcatd, sulcis numerosis ad 

 regionem ani evanentioribus ; valde inaquilaterali, crassd ; pedi-regione convexd siphoni- 

 regione major e productd, elongatd, margine dorsali depressd, concaviusculd ; umbonibus 

 elevatis obtusis ; lunula 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, l^th inch ; height, y^ths of an inch. 



Locality. Barton {Edwards). 



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 lineatissima, from Bramshaw and Brook (PL 

 XXIV, fig. 6 a, b), is, I think, a variety of this species. 



