92 INVERTEBRATA OF MASSACHUSETTS. 



an occasional darker zone ; color very pale yellowish, covered 

 with a very thin, darker epidermis, thicker and more wrinkled be- 

 hind ; in young specimens are blotches or zigzag lines of dark 

 fawn-color ; teeth well developed ; inside with very faint and 

 minute radiating lines ; margin white, the remainder bright yellow ; 

 there is always a dark purplish blotch along the posterior margin, 

 and it is sometimes mottled with bands and stains of reddish-brown 

 on other parts of the interior ; muscular impressions superficial. 

 Length of largest specimens 1 inch, height T 9 inch, breadth T 7 T 

 inch. 



Found plentifully about Nantucket, Martha's Vineyard, and 

 Rhode Island, south of which I cannot learn that it has been 

 found. 



This shell is very closely allied to the C. Icevigatum of the West 

 Indies, and has no other well marked distinction than the purple blotch 

 on the posterior margin within, which, so far as I have observed, is 

 never wanting in our species, and never present in the West India shell. 

 In the angular markings of the young shells they are similar, and also 

 in their form and color ; but the exterior of our shell is less smooth 

 and polished than C. lavigatum, a difference which might depend on 

 climate. 



CiRDiUM GRCENLANDICUM. 



Shell large, sub-triangular, drab-colored, with very numerous, 

 obsolete, radiating ridges ; slightly gaping posteriorly, beaks slight- 

 ly prominent, incurved ; margin within salmon-colored, centre 

 opaline. 



State Coll., No. 199. Soc. Cab., No. 1916. 



Cardium Groenlandicum, CHEMN. ; Conch., vi. 1. 19, f. 198. GMELIN ; Syst., 3232, 

 No. 22. BRDG.J Encyc. M6th., 222, No. 17, pi. 300, f. 7. MONTAGU: Test. 

 Brit., 29. MATON and RACKETT ; Lin. Trans., viii. 69. DILLWYN ; Catal., i. 

 129. LAM. ; An. sans Vert., vi. 407. WOOD ; Gen. Conch., 227. Index, pi. 5, 

 f.28. 



Mactra radiata, DONOVAN ; Brit. Shells, v. pi. 161. 



Cardium ed^ntulum, SOWERB?; Genera, f. 2. Conchol. Manual, f. 123*. FLEM- 

 ING ; Brit. Anim., 425. 



Aphrodite columba, LEA. ; Trans. Am. Philos. Soc., (New Series,) v. pi. 18, f. 54. 



Shell large, not very thick, sub-triangular, elevated, rather 

 compressed ; beaks not very prominent, curved inwards and 



