﻿22 



EOCENE MOLLUSCA. 



SPHENIA. Turton, 1822. 



Generic Character. " Testa transversa, inceqitivalvi, inaquilaterali, latere antico 

 hiante. Cardo valvce sinistra dente elevato transversim dilatato, decctrce dente concavo 

 cum denticulo jjostico ; lateralibus nullis. Lig amentum internum?' — Turton. 



The principal difference between this and Mya is in the impression of the mantle, 

 which in Mya has a large, broad, and deep sinus. 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. Sphenia ? angustata, /. Sowerby. Tab. B, fig. 15 a, b. 



Mya? angustata, J. Sow. Mia. Conch., t. 531, fig. 1, 1826. 



— — Morris. Catal. Brit. Foss., 2nd edit., p. 212, 1854. 



— — J. Lowry. Chart. Brit. Tert. Foss., pi. ii, 1866. 



Spec. Char. " Valves unequal ; transversely elongated, thin, antiquated, irregularly 

 compressed; extremities obtuse, gaping; lower edge of the lesser (right) valve concave." 

 — ./. Sowerby. 



Length, \\ inch ; height, f ths of an inch. 



Locality. Colwell Bay {Forbes). 



This long-known shell has a projecting process like that of Mya 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 (Panopaa) 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 Panopaa because 

 the ligament or connector is in each differently placed ; Panqpaa 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 Mya and in our present shell the connector is 

 situated within the margins, and opens the shell by expansion in opposition to the action 

 of the adductor muscles. 



