MAZATLAK BIVALVES 29 



and here and there a few radiating strife appear under the 

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

 Hah. — W. Columbia, Mus. Cum. — Mazatlan, 2 valves ; L'pool 

 Col. 



Gentts CUMINGIA, Sow. 



Por amended generic character, v. Froc. Zool. Soc. 1850, p. 24. 

 The shell differs essentially from Semele, iu its lateral teeth 

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

 mya, in its irregidar cryptophilic habits. The species here 

 enumerated are given under protest. Cumingise are nestlers, 

 like Sphfenia 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 the very variable markings. Almost aU 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 ijito 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 mercifidly for- 

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

 they are "probably somewhat variable." Locabty 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 weU as the microscope would allow me. 

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

 ber of individuals from various localities. The Mazatlan stock 

 was large enough to confuse, not to help. 



42. CUXIINGIA LAMELLOSA, SoW. 



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



Lavignon lamellosa, J5. M. Cat. D'Orh. Moll, p. 59, no. 518. 



LameUffi extremely irregular, sometimes scarcely shewmg 

 tiU the creature is nearly adidt. Eadiating stria? not strongly 

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

 terior lateral tooth the longest. 



