MAZATLAN BIVALVES 121 



170. MODIOLA CAPAX, Co?ir. 



Journ. Ac. Nat. Sc. Fhil. vol. \ii. p. 242.—JIanl. Descr. Cat. 



p. 236. 

 Modiola spinifera, P. P. C, Cat. Prov. 

 .5^?Jun.— ^lytilus spatula, Mke. in Zeit.f. Mai. 184S, p. 2. 



This specie3 having been examined at every stage, from "03 

 to 6'5 ia length, it is possible to give a tolerable account of its 

 history. It begins life as a smaU white body, shaped like 

 Anodonta, but with the umbos very^ prominent and subcentral. 

 The anteripr part is then very large, the posterior very short 

 in proportion. It soon however assumes the normal form, 

 from which (in about 60 specimens examined) it varies but 

 little. This differs from M. modiolus, ia being slightly winged 

 and strongly angled (about 130°) at the dorsal margin, and in 

 being very much produced posteriorly. The epidermis when 

 young is light green and smooth ; soon it changes to a dark 

 chesnut colour, generally developing concentric rugose u-regu- 

 lar lines, and an abundance of hairs. These, in the very young 

 shell are long, and not serrated ; but soon they become shorter 

 in proportion, very strong and hard, and armed on one side 

 with sharp, rather distant serrations. The cuticle is thin, 

 smooth and glossy on the ventral part, and inside the margin. 

 Colour at first white, tinged with purple ; afterwards vei*y 

 iridescent and shaded with flesh colour and puce, with yellow 

 near the ventral mai'gin. Ligameutal pit deeply sunken, 

 slightly bent, bounded by a strong ridge. JSTone of the Mazat- 

 lan specimens wei*e remarkable for size ; a valve however from 

 La Paz in Dr. Gould's collection measures, lomj.Q-^, lat.d' 

 alt. 2-5. 



Hab. — San Diego ; in marshes and muddy shores ; Nattall — 

 San Diego, Lieut. Green.— La, Paz, Col. Je^tJe^i!.— Gallapagos, 

 Cuminff.^S. America, [?] Kellatt, in B. M.— S. W. Mexico, 

 P. P. C. — Mazatlan ; rare, spinning a copious byssus, often 

 attached to gravel or to each other, harbouring ]\larginella, 

 CcEcum, Eulima, Odostomia, &c. ; L'pool Col. 



Tablet .554 contains 10 pairs and a minute valve, various 

 ages.— 5-55, 2 sp. adolescent.— 556, 1 do. adult'.- 557, specimens 

 of the thorny hairs. 



171. Modiola Beasiliexsis, Chemn. 



Mytilus modiolus Brasiliensis, Chemn. Conch. Cab. vol. xi, 

 pi. 205, f. 2020-1. 



Jan. 1856. ^ 



