VULSELLA. 



losity projecting within the shell, and to this conical hollow 

 the principal portion of the ligament is attached. A single 

 muscular impression only is observable in each valve ; this 

 is lateral, oblong and attenuated tovt^ards the base of the 

 shell. Vulsella differs from Crenatula principally in the 

 hinge, which has only one projecting callosity, whereas 

 that of Crenalula has many : it further differs from Ostrea 

 in not being attached, but is said to be generally, we be- 

 lieve it is always, found imbedded in sponges, to which it 

 is probably fixed by numerous rows of minute asperities 

 on its outer surface, in the same manner as Acasta, among 

 the Cirripedes, is by the small hooked spines of its six 

 valves. Having in our possession several specimens of 

 Vulsellae in their native situation, we think we may safely 

 affirm that it is not attached by any byssus ; though, as 

 Lamarck well observes, they are sometimes a little gaping 

 posteriorly. The shell, as in all cognate genera, is com- 

 posed of two substances, one internal and pearly, the other 

 external and consisting of laminae formed of perpendicular 

 fibres. On account of the irregularity of the shells of this 

 genus, we think it must be extremely difficult to distinguish 

 the species, and, consequently, we believe that several mere 

 varieties are raised to the rank of species. Lamarck de- 

 scribes six, which are recent^ differing from each other in 

 size^ colouring and form ; all characters of minor import- 

 ance, particularly in irregular shells. He also mentions 

 one fossil species, found at Grignon, 

 We have given representations. 



Fig. 1. & 2. Of tlie inside and outside of a specimen of Vulsella lingulata, of 

 Lam. — Mya* Vulsella, Linn, commonly called the Hounds-ear Oyster, 

 from the Indian Ocean ; a shell much esteemed in this country, on 

 account of its rarity. 



3. A single specimen in a sponge; and 



4. A group of small ones, which we believe to be a variety, and the 



younger state of the same species. 



♦ We have not pointed out the differences between this Genus and 3fya, 

 because it is not in the slightest degree related to it. 



