146 GASTROCH^NIDifi. 



S. uuGosA, Linnaeus. 



Anterior extremity usually broad and rounded, no decided 

 lunule-like excavation in front of the beaks ; posterior extremity 

 frequently the narrower, ligamental edge rarely much incurved, 

 more often convex ; linear ridges only spinous in the young shell ; 

 hinge margin of the mature shell edentulous. 



Plate VI. figures 7, 8, and (Animal) Plate F. fig. 6. 



Myiilus riu/osus, Penn. Brit. Zool. ed. 1, vol. iv. p. 1 10, p. 63, f. 72. — Pulteney, 

 Hutchins Dorset, p. 37. — Mont. Test. Brit. p. 164. — Donov. 

 Brit. Shells, vol. iv. p. 141. — Linn. Trans, vol. viii. p. 105. — 



Dorset Catalogue, p. 39, pi. 13, f. 5 Turt. Conch. Diction. 



p. 113. — DiLLW. Recent Shells, vol. i. p. 304. — Index Testa- 

 ceolog. pi. 12. My til. f. 9. 

 MytUuspholadiSyhi^s. Mantissa? p. 548. — Muller, Zool. Danica, pi. 87, f. 



1, 2, 3. 

 Alya hyssifcra, 0. Fabric. Fauna Greenland, p. 408. 



Saxicava rugosa. Lam. Anim. s. Vert. ed. 2, vol. vi. p. 152. — Turt. Dithyra 



Brit. p. 20, pi. 2, f.lO.— Macgilliv. Moll. Aberd. p. 285.— 



Brown, Illust. Conch. G. B. p. 103, pi. 47, f. 14, 16.— 



Crouch, Introd. Conch, pi. 5. f. 3. — Sowerby, Genera 



Shells, Saxicava, f. 2, 3, 4. — Reeve, Conch. Icon. vol. i. pi. 



50, f. 2, 3, 4.— Hanl. Recent Shells, p. 50. 



Saxicava GaUicana, Lam. Anira. s. Vert. ed. 2, vol. vi. p. 152. — Deles. Rcc. 



Coq. pi. 4, f. 9.— Desh. Elem. Conch, pi. 12, f. 1, 2, 3.— 



Hanl. Recent Shells, suppl. pi. 9, f. 5. 



Saxicava pholadis. Lam. Anim. s. Vert. ed. 2, vol. C, p. 152. — Ti'rt. Dithyra 



Brit. p. 21, pi. 2, f. 11.— Hanl. Recent Shells, p. 50. 

 Sacricaixi distorta, Gould, Invert. Massach. p. 61, f. 40. 

 Bi/ssoniya pJioladis, BowDicii, Bivalves, f. 43. 

 Hiutella iihlomja, (young) Turt. Dithyra Brit. p. 25, pi. 2, f. 13. 

 Hiatella ruyosa, Flem. Brit. Anim. p. 4G1. — Brit. Marine Conch, p. 58. 

 Saxicave ridee, Chenu, Traite Elem. p. 58, f. 197, 198. 



There scarcely exists a molluscous animal, whose tes- 

 taceous covering is more affected by circumstances of habi- 

 tation, than this ancient and widely extended species. 

 Subject to almost every distortion of shape, it has received 

 several appellations. The valves, when uninterruptedly 

 developed, are generally of an oval-oblong shape ; they are 

 solid, ventricose, opaque, white, covered with a dull or 



