MAZATLAN BIVALVES 29 



and here and there a few radiating striae appear tinder the 

 microscope. Long. *28, lat. "34, alt. "13. 



Hab.W. Columbia, Mus. Cum. Mazatlan, 2 valves ; ISpool 

 Col 



GENUS CUMINGIA, Sow. 



For amended generic character, v. Proc. Zool. Soc. 1850, p. 24. 

 The shell differs essentially from Semele, in its lateral teeth 

 and ligamental spoon. The animal also differs, as from Syndos- 

 mya, in its irregular cryptophilic habits. The species here 

 enumerated, are given under protest. Cumingise are nestlers, 

 like Sphaenia and Saxicava, and therefore subject to every possi- 

 ble variation of form. They are fond of growing in company, 

 and squeeze each other up into the queerest shapes. And yet 

 the published specific characters are mainly drawn from the 

 shape alone, with th,e very variable markings. Almost all the 

 species are variously ribbed concentrically, with minute radiat- 

 ing decussations. The characters of the hinge may be more 

 constant; but alas! neither Sow. nor A. Ad. even allude to them. 

 I have examined about 60 specimens from Mazatlan which 

 might easily be distributed into 20 species, with as good char- 

 acters as those which distinguish Sow.'s species. C. B. Adams 

 distributed his 14 specimens into 6 species, but mercifully for- 

 bore to describe the 4 supposed new ones, on the ground that 

 they are "probably somewhat variable." Locality also is no 

 great help : the Atlantic and Pacific, the N. and S. Temperate 

 species not differing from each other so much as each species 

 may within itself. Mr. Cuming has most kindly come to my 

 rescue, and named the principal specimens according to his 

 types : the smaller ones, in which there is least distortion, I 

 have mapped out as well as the microscope would allow me. 

 To do the work satisfactorily would require a very large num- 

 ber of individuals from various localities. The Mazatlan stock 

 was large enough to confuse, not to help. 



42.'CtTMINGIA LAMELLOSA, Sow. 



Proc. Zool. Soc. 1833, p. 34. 



Lavignon lamellosa, _R M. Cat. _D' Orb. Moll, p. 59, no. 518. 



Lamellae extremely irregular, sometimes scarcely shewing 

 till the creature is nearly adult. Radiating striae not strongly 

 marked. Pallial sinus moderate : hinge teeth moderate, pos- 

 terior lateral tooth the longest. 



