274 MOLLUSCA, 



them are relieved with scales. The Limse swim with rapidity by means of 

 their valves. 



Certain fossils may be placed here which have the hinge, ligament, 

 and central muscle of the Ostreas, Pectines, and Limse, but are dis- 

 tinguished by some of the details of the shell. They are Hinnitay 

 Plagiostoma, Pachytes, Dianchora^ and Podopsis. 



Although multivalve, we should approximate the 



Anomia, Brug. 

 To the Ostreae. The Jnomise have two thin, unequal, irregular valves, the 

 flattest of which is deeply notched on the side of the ligament, which is 

 similar to that of the Ostrere. The g-reater part of the central muscle tra- 

 verses this opening to be inserted into a third plate, that is sometimes stony 

 and sometimes horny, by which the animal adheres to foreign bodies, and 

 the remainder of it (the muscle) serves to join one valve to the other. The 

 animal, — Echion, Poll, has a small vestige of a foot, similar to that of a 

 Pecten, which slips between the emarginatlon and the plate that closes it, 

 and perhaps serves to direct water to the mouth, which is close to it. 



These shells are found attached to various bodies hke the Ostreae. They 

 are found in every sea. 



PiiACUNA, Brug. 



A small genus allied to the Anomlse, in which the valves are thin, unequal, 

 and frequently irregular, as in the latter, but both entire. 



SpoNDYiiUS, Lin. 

 A rough and foliaceous shell like the Ostrea, and frequently spiny; but 

 the hinge is more complex? besides the cavity for the ligament, analogous 

 to that of the Ostreae, there are two teeth to each valve that enter into 

 fossx in the opposite one; the two middle teeth belong to the most convex 

 valve, which is usually the left one, and which has a projecting heel, flat- 

 tened, as if sawed thi-ough behind the hinge. 



The Spondyli are eaten hke Oysters. Their shells are frequently tinged 

 with the most brilliant colours. They adhere to all sorts of bodies. 



Malleus, Lam. 

 A simple pit for the ligament as in the Ostrese, where the Mallei were left 

 by Linnaeus, on account of their having the same irregular and inequlvalve' 

 shell, but distinguished by a notch on the side of this ligament for the pass- 

 age of a byssus. 



The most known species, Ostrea malleus, L. , which ranks among the num- 

 ber of high-priced and rare shells, has the two ends of the hinge extended 

 and forming something hke the head of a hammer, of which the valves. 



