MAZATLAN BIVALVES 9 
16. PHoLADIDEA ?curRTA, Sow. 
Pholas curta, Proc. Zool. Soc. 1834, p. 71.—B. M. Cat. D Orb. 
Shells, no. 482, p. 56. 
The only two specimens found are too imperfect to identify 
with accuracy. Though very small, they are both adult, and 
are known at once from the young of melanura by the extreme 
fineness of the anterior waved stiri, the posterior part scarcely 
shewing more than lines of growth. Dorsal plate shield-shaped, 
in two layers, hollow within, rather large and regular. Long. °28, 
lat. °34; shield ‘17 by °15. 
Hab.—Isle of Lions, Veragua, in soft stone at low water, Cum- 
ing.—Kcuador : Isle de los Leones, |? |D’ Orbigny.—Mazatlan, 
in Strombus galea, Havre Col. 
Tablet 22 contains 1 valve (the other being broken in extrac- 
tion) with its plate. 
Genus PARAPHOLAS, Conr. 
Parapholas, Conrad. sp. 
This genus, including Californica, Incii (Torres Str.), branchi- 
ata, calva, (acuminata,) and bisuleata (Woodw.) differs from 
Martesia (Leach) in having its cup lamin persistent and under- 
lapping one another. It further differs from Pholadidea in 
the large size of the umbonal plate, and the gaping in the ven- 
tral and dorsal margins, closed by plates in the adult shell. All 
yet known are from the Pacific. The Californian species is of 
large size, and makes a shelly tube for its siphons. 
17. PARAPHOLAS CALVA, Gray, ms. 
Pholas calva Sow. in Proce. Zool. Soc. 1834, p. 69.—Thes. Conch. 
1849, p. 493. 
Animal excavating a pear-shaped burrow in shell (or stone) 
which is perfectly smooth and circular transversely, so that the 
shell ‘(till it becomes adult) can move freely round in it. The 
orifice is subcircular, and rather large. As the animal continues 
its boring deeper, the swollen anterior portion becoming now 
posterior and therefore too large for the animal, which loves to 
have just room enough and no more, the vacant space is filled 
up with a lining (more or less thick according to the depth of 
the burrow) which is not an organic growth from the mantle, 
but appears to be nothing more than a sedimentary deposit 
in layers. Whether the burrow is in the purple or white 
portion of the Spondylus, the deposit is always dark grey. 
Jt may be detached as a tube from the cavity, and is often per- 
