464 CTPRINIDiE. 



gillivray); and a fresh single valve has likewise been 

 dredged in eighty fathoms water, forty miles to the west of 

 the Mainland of Zetland (E. F. and M'Andrew). The 

 beautiful and perfect specimen delineated in our engraving 

 was procured from Loch Riden by Capt. Brown, to whose 

 courtesy we are indebted for the loan of it. 



It is a strictly boreal shell, and is chiefly obtained from 

 Spitzbergen and Sweden, but is by no means common in 

 the museums and private collections of England. The 

 A. semisulcafa of Leach (Appendix to Ross's Voyage), of 

 which the young was figured in the Supplement to the "In- 

 dex Testaceologicus," under the name of Mactra Veneri- 

 formis (we speak from an examination of the original types), 

 is most closely allied to this species, but is generally more 

 elliptical in shape, has broader and more manifest umbonal 

 plicse, eroded umbones (in the adult), and a somewhat 

 different-looking epidermis. It occurs fossil in pleistocene 

 strata of Britain, Northern Europe, and Boreal America. 



A. coMPEEssA, Montagu. 



Small, subtriangular, subequilateral, usually as broad as 

 long, never elliptical ; either traversed concentrically and en 

 tirely with most crowded and very narrow costellae, or smooth, 

 excepting at the beaks, which are always thus costellated. Epi- 

 dermis yellowish or olivaceous, never chestnut nor fibrous, glossy. 

 Beaks very prominent and acute. Ventral margin quite entire. 



Plate XXX. fig. 1, 2, 3. 



Venus coinpressa, Mont. Test. Brit. Suppl. p. 43, pi. 26, f. 1. 



Venus Montagui, Dillw. Recent Shells, vol. i. p. 167. — Turt. Conch. Diction. 



p. 243.— Index Testaceol. pi. 7, f. 19. 

 Cyprina compressa, Turt. Dithyra Brit. p. 137, pi. 11, f. 22, 23. 

 Astafte compressa, Flem. (not Macgil.) Brit. Anira, p. 440. 

 Crassina Montu(jui,(jKA\', Km\. Phil. 1825, p. 13C. — Hanl. Recent Shells, vol. i. 



p. 88. 

 Astarie striata, Brown, 111. Conch. G. B. p. 9G, pi. 38, f. (I, 7, 8. — Loven, Index 

 Moll. Skandinavise, p. 37. 



