BIVALVIA. 187 



Length, -|^ths of an inch : heiglit, f ths ditto. 



Locality. Mam. Crag, Bridlington. Recent, Britain. 



One specimen only of this species has come under my observation, it was found by 

 Mr. Leckenby, who has obligingly permitted me to have it figured. 



If it were in almost any other genus than the present, the differences between this 

 shell and the figure and description given, above referred to, might, perhaps, be 

 sufficient to justify its being considered a new species ; but with only a single specimen, 

 I am unwilling to do more than refer it to one already established. Our present shell 

 may be further particularised as having a prominent and sharp umbo curving a little 

 over a lunule, large and deep ; the ridges upon the exterior are large, somewhat 

 prominent and rounded, about as wide as the spaces between them, and on the anterior 

 side they extend up to the lunule, and there stop rather abruptly ; while on the 

 posterior side, in the young state, they reach to the edge of the corselet, becoming 

 obsolete and nearly smooth down the slope in the older part of the shell ; our specimen 

 is more equilateral, less broad posteriorly, and of a more triangular form than the 

 figures above referred to, but in other respects there is so great a resemblance that 

 it may be considered as probably an aberrant form of the above species. The 

 lunule and corselet are smooth, or, at least, show only lines of growth, and the 

 numerous and close set ridges seem to remove it from any specific connection with 

 A. sulcata. 



A fossil in the Cabinet of Mr. Morris, brought from the mouth of the Varga, 200 

 miles up the Dwina, by Sir Roderick Murchison, more resembles the figure and 

 description of crebricostata in the ' Hist, of Brit. MoUusca.' 



15. AsTARTE PYGM^A, Ilunster. Tab. XVII, fig. 7 a — h. 



AsTABTE PYGM^A. (Munst.) ex Gold/. Pet. Germ., vol. ii, p. 195, t. 135, figs, 5, 6 a, b ; 



(excl. syn.) 

 — — S. Wood. Catalogue, 1840. 



Spec. Char. Testa minufd, orhiculato-trigond, compressiusculd, equilaterali, umhonihus 

 prominulis ; concentrice costatd, costis crebris, conveccis ; margine crenato vel integro. 



Shell small, roundedly trigonal, somewhat compressed, equilateral ; umbones 

 slightly prominent, concentrically costated ; ridges thick, numerous, and convex ; 

 margin crenulated or smooth. 



Diameter, \\h of an inch. 



Locality. Cor. Crag, Sutton. 



This species is exceedingly abundant at the above locality, but the valves are 

 rarely found united. It appears to correspond with the figure and description by 

 Goldfuss. 



Our shell has the posterior dorsal edge somewhat rounded, and the longitudinal 

 diameter generally exceeds the height; the umbo is neither very sharp, nor very 



