mazatlan bivalves 9 



16, Pholadidea Pcueta, Sow. 



Pholas curta, Proc. Zool. Soc. 1834, p. 71— 5. M. Cat. D'Orb. 

 Shells, no. 482, p. 56. 



Tke only two specimens found are too imperfect to identify 

 witli accuracy. Tliougk very small, tliey are both adult, and 

 are known at once from the young of melanwra by the extreme 

 fineness of the anterior waved striae, the posterior part scarcely 

 shewing more than Hues of growth. Dorsal plate shield-shaped, 

 in two layers, hollow withui, rather large and regular. Long. '28, 

 lat. -34; shield -17 by 'lo. 



Sab. — Isle of Lions, Veragua, in soft stone at low water, Cum- 

 ing. — Ecuador : Isle de los Leones, [f^D' Orbigni/. — Mazatlan, 

 in Strombus galea, Swore Col. 



Tablet 22 contains 1 valve (the other being broken in extrac- 

 tion) with its plate. 



Genus PAEAPHOLAS, Conr. 

 Parapholas, Conrad, sp. 



This genus, including Califomica, Incii (Torres Str.), branchi- 

 ata, calva, (acuminata,) and bisulcata (Woodw.) differs from 

 Martesia (Leach) in having its cup laminae persistent and tmder- 

 lapping one another. It further differs from Pholadidea in 

 the large size of the \imbonal 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 shellj^ tube for its siphons. 



17. Paeapholas calva, Gray, ms. 



Pholas calva Sow. in Proc. Zool. Soc. 1834, p. 69. — TJies. 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 dei)th 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 puiiile or white 

 portion of the Spoudylus, the deposit is always dai'k grey. 

 It may be detached as a tube from the cavity, and is often per- 



