BIVALVIA. 181 



From the specimens of the American shell, and from the representations that I have 

 seen, I was inclined to consider them distinct from the peculiarly angular extremity 

 of the posterior side. 



This species in the adult state has the margin thickened within and roughly 

 crenulated, although in some large specimens this character is not seen. In all 

 specimens the shell in its young state is covered externally with broad and deep 

 furrows, and is much compressed, and it is in the older shell that it becomes so variable ; 

 these ridges or furrows are in some limited to a rather small space upon the surface, 

 or what may be called the umbonal region, while in others the surface is covered with 

 them entirely ; these latter continue generally much compressed, while those which 

 have the surface, or at least the greater part of it, quite smooth, and comparatively 

 short, are very tumid, the lunule and corselet in that case becoming of course very 

 large ; the posterior side is always more or less truncated, and the umbo sharp, often 

 much pointed. The rugae spoken of by Sir Charles Lyell as so conspicuous upon the 

 teeth, at least on the outside of the large cardinal tooth of the right valve, and the 

 corresponding inside of the two teeth in the left valve of the American shell, are 

 visible enough in well-preserved specimens of the English fossil, but these markings 

 are no good specific character, and may be seen in several other species. I have 

 traced this species down to the young shell, with a diameter little more than the eighth 

 of an inch, when the cardinal tooth extends to the umbo, but as the shell enlarges, 

 these teeth proceed forward, leaving a space between them ; the beaks stand up 

 prominent and sharp, but do not touch, and the opening of the valves is carried 

 backwards by a somewhat extended ligament. 



8. ASTARTE ELLIPTICA, Brown. Tab. XVI, fig. 7. 



CRASSINA ELLIPTICA. Brown. Illust. Brit. Conch., pi. xviii, fig. 3, 1827- 



OVATA. Id. Edinb. Journ. Nat. and Geogr. Sci., vol. i, p. 12, pi. i, 



figs. 8, 9. 

 Id. Illust. Brit. Conch., 2d ed., p. 96, pi. xxxviii, figs. 12, 13. 



DEPRESSA. Id. p. 96, pi. xxxviii, fig. 2. 



STJLCATA. Nikon. Nov. Act. Holm., p. 187, pi. ii, figs. 1, 2, fide Forb. and Hani. 



GAIRENSIS. Smith. Mem. Wern. Soc., vol. viii, p. 42. 

 ASTARTE ELLIPTICA. Macgill. Moll. Aberd., p. 259, 1843. 



Alder. Catal. Moll. North, and Durh., p. 87, 1848. 



Forb. and Hani. Hist. Brit. Moll., vol. i, p. 459, pi. xxx, fig. 8, 1848. 



GAIRENSIS. W. Nicol. MS. 



Morris. Catal. Brit. Foss. p. 79, 1843. 



SEMISULCATA. Moller. Ind. Moll. Groenl., p. 19, 1842. 



Phil. Neuer. Conch., vol. ii, p. 57; Astarte, pi. i, fig. 10. 



Lavtn. Ind. Moll. Scand., p. 37, 1846. 



Spec. C/tar. Testa transversd, ettipticd, incequilaterali, compressiusculd; postice longiore, 

 truncatd, semisulcatd; lunuld profundd, lanceolato-cordatd ; margine integerrimo. 



