316 CYPRINID^E. 



a bevelled edge: pallial and miiscular scars as in the last 

 species, but the latter are more deep. L. 0-5. B. 0-5. 



Var. 1. globosa. Shell much larger, and usually more con- 

 vex, inclining to a circular shape, with fine and regular ribs, 

 which in the adult generally disappear towards the front and 

 sides. L. 0-8. B. 0-9. A. globosa, Holler, Ind. Moll. Grcenl. 

 p. 20. 



Var. 2. striata. Shell more closely ribbed. A. striata 

 (Nicania striata, Leach), Moll. 1. c. 



Var. 3. nana. Shell much smaller, either smooth or partly 

 ribbed. L. 0-225. B. 0-225. 



HABITAT : Sand, often mixed with mud, in 20-50 

 fathoms, off Scarborough (Bean), and Mull (Bedford) : 

 the typical form appears to be very local. Subfossil in 

 25 fathoms off Larne, co. Antrim. Var. 1. Rather 

 common off Skye, the coasts of Argyle and Ross, and 

 east of Shetland, in 30-80 fathoms. It resembles in 

 shape Corbicula (or Cyrena) fluminalis. Var. 2. Plen- 

 tiful on the coasts of Yorkshire, Northumberland, and 

 Durham, Firth of Forth, west of Scotland, and outer 

 Hebrides, in sand and mud, at from 3 to 50 fathoms. 

 This variety occurs in all our newer tertiaries, as far 

 back as the Red Crag ; and it is peculiar to the glacial 

 deposits. Var. 3. Fifteen miles N.W. of Mull (Bed- 

 ford). It seems to present a link connecting the pre- 

 sent with the next species. A. compressa, and parti- 

 cularly the variety striata, are extensively distributed 

 throughout the North Atlantic from Spitzbergen and 

 the White Sea to the Cattegat, as well as on the north- 

 eastern coasts of America, at depths varying from 10 to 

 140 fathoms. It is found in the Uddevalla and other 

 similar deposits in Scandinavia ; Risso has recorded it, 

 under the name of Cyprina Montagui, as fossil in the 

 " terrains diluviens " at Nice ; and Drexler found it in 

 " pliostene " strata in Hudson's Bay. 



