781 



thick and tumid, some thinner, flatter, and more eUiptical, I came 

 to this conclusion, that either each specimen must be a species, 

 or that they must all be one. The general smoothness of surface 

 towards the margin, the irregular obsolete corrugations near the 

 beaks, and the thin margin, and its smooth inside margin being 

 alike in all, decided me to adopt the latter alternative, as others 

 have done. 



Northern Seas. 



8. AsTAUTE SEMisuLCATA (pi. clxvii. f. 16), Leach. Crassina 

 semisulcata, Ann. Phil. xiv. f. 204. 



Ast. testa compressa, Isevi, elongata, prope umbones leviter 

 concentrice sulcata; margine interno leevi. 



If this shell, which I have from Mr. Hanley, be the true C. 

 semisulcata of Leach, it will occupy the same position with regard 

 to A. Arctica as A. eUiptica does to A. sulcata, its chief distinc- 

 tion being its great elongation of form. 



North Seas. 



9. AsTARTE LACTEA (pi. clxvii. f. 21, 22, 23), Brodenp, 

 Zool. Journ. iv. p. 365. 



Ast. "testa obovata, compressa, antice breviore; margine dor- 

 sali postico depresso ; intiis lactea, marginibus integerrimis." 



Like A, Arctica, but with strong and regidar costellae near the 

 apices. The epidermis is often, when fully developed, very thick 

 and black, and the shell very white within ; margins smooth. The 

 species is subject to the same variation as the last. 



North Europe. 



10. AsTARTE OBLONGA (pi. clxvii. f, 19), Soiocrhi/, jtm. 



Ast. testa inflata, ovali, tenui, antice et ad medium concentrice 

 minute lirata, postice longiore, tenuistriata ; cardine angusta ; mar- 

 gine ventrali crenato. 



An oval, rather hght, inflated shell, with numerous small con- 

 centric ridges commencing on the anterior side, and dying out a 

 little past the middle, the hinder side being nearly smooth or 

 slightly striated. The lunule and dorsal area are impressed as 

 usual, and of a distinct chestnut-colour compared to the rest of 

 the epidermis, which is light oHve. Inside white; hinge thin, 

 margin arcuated. 



Hab. ? Mr. Cuming's collection. 



11. AsTARTE Banksii (pi. clxvii. f. 8), Leach, Eoss Voy. 



