80 INVERTEBRATA OE MASSACHUSETTS. 



has arrived at its full dimensions, and the margin of the valves begins 

 to thicken, as it always does ; and then, so far as my observation goes, 

 there is always a crenulated margin ; so that this is merely a mark of 

 maturity. 



In the next place, Turton and others, with apparently good reasons, 

 conclude, that the sulcata and the Danmonia are the same. It is cer- 

 tain, that Montagu's figure of Danmonia^ and Turton's of sulcata, in 

 his " British Bivalves," represent precisely the same shell. Turton, 

 however, has fallen into Montagu's error of making two species, the 

 ScStica and sulcata, which he says are precisely alike 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. The figure of V. sulcata in the " Linnaean Trans- 

 actions," pi. 2, f. 2, and even its description, would apply better to our 

 A. castunca, than to the shell in question. 



Two pretty well mai'ked groups of this furi'owed 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 marked, epidermis very dark greenish-yellow. Some 

 of them are quite inequilateral, and occasionally the undulations vanish 

 not far below the summit, and the remainder of the surface is merely 

 wrinkled. These do not correspond with any British shells or figures 

 1 have seen. They may possibly prove to be distinct ; and, if so, I 

 would name them A. undata. 



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 upwards, and 

 of course more crowded ; the epidermis is dark yellowish-brown, or 

 piceous. These, I regard as the true A. DanmonUnsis. They agree 

 with the figures of Montagu and Turton, and with the outlines given 

 by Colonel Totten. 



ASTARTE LACTEA. 



Shell sub-orbicular, much compressed, concentrically wrinkled, 

 epidermis yellowish-brown ; an obsolete marginal tooth in each 

 valve ; margin plain. 



ElGURE 47. 



State Coll., No. 203. Soc. Cab., No. 1804. 



Astarte lictea, Brod. and S'owekby ; Zool. Journ.,i\ 3G5. Jlppcndix to Beechcij's 

 Voyage, pi. 44, f. I'2. 



