MAZATLAN BIVALVES 121 
70. MopioLa capax, Conr. 
Journ. Ac. Nat. Se. Phil. vol. vu. p. 242.—Haznl. Descr. Cat. 
p. 236. 
Modiola spinifera, P. P. C., Cat. Prov. 
??Jun.—Mytilus spatula, i/ke. in Zeit. f, Mai. 1848, p. 2 
This species having been examined at every stage, from “03 
to 6°5 in length, it is possible to give a tolerable account of its 
history. It begins life as a small white body, shaped like 
Anodonta, but with the umbos very prominent and subcentral. 
The anterior 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, in 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 irregu- 
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 euticle is thin, 
smooth and glossy on the ventral part, and inside the margin. 
Colour at first white, tinged with purple; afterwards very 
iridescent and shaded with fiesh colour and puce, with yellow 
near the ventral margin. lLigamental pit deeply sunken. 
slightly bent, bounded by a strong ridge. None of the Mazat- 
lan specimens were remarkable for size; a valve however from 
La Paz in Dr. Gould’s collection measures, long. 6°5, lat. 3°, 
alt. 2°5 
Hab.—San Diego; in marshes and muddy shores ; Wuttali— 
San Diego, Lieut. Gr een. —La Paz, Col. Jewett. Bees. 
Cuming. af America, [? | Kellatt,in B. M.—S. W. Mexico, 
P. P. C—Mazatlan ; bee spinning a eae besea otten 
attached to gravel or to each other, harbouring Marginella, 
Coecum, Eulima, Odostomia, &e.; Z’poel Col. 
Tablet 554 contains 10 pairs and a minute valve, various 
ages.—ddd, 2 sp. adolescent.—556, 1 do. adult.—557, specimens 
of the thorny hairs. 
171. Mopiots Brasitrensis, Chemn. 
Mytilus modiolus Brasiliensis, Chemn. Conch. Cab. vol. xi. 
pl. 205, f. 2020-1. : 
Jan. 1856. m 
