eo 
co) 
EOCENE MOLLUSCA. 
SPHENIA. Turton, 1822. 
Generic Character. ‘‘ Testa transversd, inequivalvi, inequilaterali, latere antico 
hiante. Cardo valve sinistre dente clevato transversim dilatato, dextre dente concavo 
cum denticulo postico ; lateralibus nullis. Ligamentum internum.” —Turton. 
The principal difference between this and J/ya is in the impression of the mantle, 
which in J/ya has a large, broad, and deep smus. Messrs. Forbes and Hanley have 
given a representation of the animal inhabitant, which shows it to be different from that 
of Mya. There is also a difference in the dental furniture of the shell, the projecting 
support for the connecting ligament being more extended backwardly in the left valve, 
while in the right one there is a distinct denticle. 
1. Spoenta ? ancustata, J. Sowerby. ‘Tab. B, fig. 15 a, 6. 
Mya? aneustara, J. Sow. Min. Conch., t. 531, fig. 1, 1826. 
— — Morris. Catal. Brit. Foss., 2nd edit., p. 212, 1854. 
— — J. Lowry. Chart. Brit. Tert. Foss., pl. ii, 1866. 
Spec. Char. “ Valves unequal ; transversely elongated, thin, antiquated, irregularly 
compressed ; extremities obtuse, gaping; lower edge of the lesser (right) valve concave.”’ 
—J. Sowerby. 
Length, \+ inch ; height, 3ths of an inch. 
Locality. Colwell Bay (Fordes). 
This long-known shell has a projecting process like that of JZya truncata, on which the 
cartilaginous connector is placed, but not exactly of the same form; and the sinus made 
by the mantle is smaller, comparatively, and less deep than in Mya. Mr. Morris, when 
describing what is a closely allied species, if it be not indeed a variety of the same shell, 
in the Geological Survey Memoir upon the geology of the Isle of Wight, has given to it 
the name of Mya (Panopea) minor, of which he gives two varieties. I feel at a loss what 
generic name to give to this shell, but it cannot be placed among the Panxopee because 
the ligament or connector is in each differently placed; Panopea having a projecting 
ledge on the outside of the dorsal margin for the support of the connector, which acts by 
elongation and contraction ; whereas in M/ya and in our present shell the connector is 
situated within the margins, and opens the shell by expansion m opposition to the action 
of the adductor muscles. 
