MAZATLAN BIVALVES 29 
and here and there a few radiating strie appear under the 
microscope. Long. °28, lat. °34, alt. °13. 
Hab.—W. Columbia, Mus. Cum.—Mazatlan, 2 valves; D’pool 
Col. 
Genus CUMINGIA, Sow. 
For amended generic character, ». 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. Cumingie are nestlers, 
like Spheenia 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 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 8. 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, 1 
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. CUMINGIA LAMELLOSA, Sow. 
Proc. Zool. Soc. 1833, p. 34. 
Lavignon lamellosa, B. WM. Cat. D’ Orb. Moll, p. 59, no. 518. 
Lamelle extremely irregular, sometimes scarcely shewing 
till the creature is nearly adult. Radiating strie not strongly 
marked. Pallial smus moderate: hinge teeth moderate, pos- 
terior lateral tooth the longest. 
