Mr. E. A. Smith on the Genus Sphenia. 277 
XLIX.— Observations on the Genus Sphenia, with Descriptions 
of new Species. By Epcar A. SMITH. 
[Plate XV. A.] 
THE genus Sphenia was originally founded by Turton * in 
1822 for the well-known S. Bingham?t. It was founded on 
conchological grounds only, and it was not until 1853 ¢ that 
an account of the soft parts was published. The genus has 
relationship, either as regards the shell or the animal, with 
Mya and Corbula; indeed it is considered synonymous with 
the former by Jeffreysf. On the other hand, M. Petit § 
upholds its validity, observing that it differs from J/ya by its 
thin shell, which is less gapmg behind and very inequivalve. 
The animal has relatively short siphons, and, at the base of 
the foot, a true byssus. ‘The Sphenias live attached in holes 
in rocks, whilst the Mye rest buried in the sands, 
Mr. Clark ||, although admitting the genus, appears to have 
found very slender reasons for so doing. He observes :— 
“This animal has great aflinity to Saaicava, besides alliances 
with Corbula and Mya; indeed, the genus Sphenda is almost 
unnecessary, and its animal is nearly identical with Savicava 
arctica, and the structure of the hinge and the other hard 
parts have much the same generalities.’ 
Sphenia is admitted as a distinct genus by Forbes and 
Hanley, Tryon, Fischer, H. and A. Adams, and others. It 
is united with J/ya by Jeffreys, and considered as a subgenus 
of Corbula by Philippi and Woodward. 
After careful consideration I am inclined to agree to the 
separation of this genus. Besides the differences between it 
and Mya pomted out by M. Petit it is worth noting that all 
the species at present known are very small in comparison 
with the A/ye. 
M. Petit refers to the presence of a byssus asa distin- 
guishing character; but I would point out that Mya in the 
young stage also secretes that appendage J. 
Corbula dees not form a byssus, and, judging from the 
C. gibba, the siphons appear to be shorter than in Sphenia ; 
also, hike Mya, it lives buried in sand or mud, not in holes in 
rock like Sphenia. 
* Conch. Ins, Brit. p. 36. 
t Forbes and Hanley, Brit. Moll. i. pp. 189-193. 
} Brit. Conch. iii. pp. GO and 70. 
§ Cat. moll. test. Europ. 1869, p. 245. 
| Brit. Marine ‘Test. Moll. (1855), p. 150. 
{| Jeffreys, Brit. Conch, vol. iii, p. 66. 
