AST ARTE. 121 



margin, until the shell has arrived at its full dimensions, and the 

 margin of the valves begins to thiclven, as it always docs ; and then, 

 so far as my observation goes, there is always a crenulated margin ; 

 so that this is merely a marlc of maturity. 



In the next place, Turton and others, with apparently good rea- 

 sons, conclude that the sulcata and the Danmonia are the same. 

 It is certain that Montagu's figure of Danmonia, and Turton's of 

 sxlcdfa, in liis '" British Bivalves," represent precisely the same 

 shell. Turton, however, has fallen into Montagu's error of making 

 two species, the Scotica and sulcata, which he says are precisely 

 alilvc in all respects except the margin. Both the figures accurately 

 represent one of the forms found on our coast, and that which might 

 be regarded as the intermediate form. 



Two ])retty well marlvcd groups of this furrowed species may be 

 made out. One in which the shells are somewhat elongated, and 

 pointed posteriorly, of an oval shape, undulations about fifteen, and 

 very strongly marl^ed, epidermis very dark greenish-yellow. Some 

 of them are quite inequipartite, and occasionally the undulations 

 vanisli not far below the summit, and the remainder of the surface 

 is merely wrinkled. These do not correspond with any British 

 shells or figures I have seen. They may possibly prove to be dis- 

 tinct ; and, if so, I would name them A. t/ndata. 



In the other group the shell is rounded, the beaks nearly central, 

 broad posteriorly, and usually a little blunted or truncated at the 

 point; the undulations are much more numerous, twenty and up- 

 wards, and of course more crowded ; the epidermis is dark ycllow- 

 ish-ljrown, or piceous. These I regard as the true A. Danmonien- 

 sis. They agree with the figures of Montagu and Turton, and with 

 the outlines given by Colonel Totten. 



Astarte semisulcata. 



Fig. 47. 



Shell sub-orbicular, compressed, concentrically wrinkled, epidermis yellowish- 

 brown ; an oljsolete marginal tooth in each valve ; margin plain. 



Crasslna semisuJrafa, Leach, in Ross's Voy- Append. 175. 



Astarte arcticci, FoHB^ES, and Hanl. I5r. Moll. i. 4G1, t. 30, fig. 7. — Sowerby, Thcs. 



Conch ii. 780, t. 67, figs. 17, 18, 20. 

 Astarte semisulcata. Gray, Cat. Br. M. (Br. Biv. ) 92. 



Crassina airtira, Gray, Append, to Parry's Voy. — IIanlet, Recent Sliclls, i. 88. 

 Astarte borenlis, Philippi, Abbild. ii. 58 (Astarte), t. 1, fig. 11. — McAnd. and Forbes, 



Ann. Nat. Hist. xix. 98 {1847). — Forbes, Mem. Geol. Survey, i. 412. 



