ACEPHALA TESTACEA. 261 



PECTF.N, Bruguieres. 



The Pectens, very properly separated from the Oysters by Bruguieres, 

 although they have the same kind of hinge, are easily distinguished by their 

 inequivalve semi-circular shell, almost always regularly marked with ribs 

 which radiate from the summit of each valve to the edge, and furnished with 

 two angular productions called ears, which widen the sides of the hinge. 



LIMA, Bruguieres. 



The Lima; differ from the Pectens in the superior length of their shell in 

 a direction perpendicular to the hinge, the ears of which are shorter, and the 

 sides less unequal, thus forming an oblique oval. The ribs of most of 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 Ostrese, Pectines, and Limae, but are distinguished by 

 some of the details of the shell. They are Hinnita, Plagiostoma, Pachytes, 

 Dianchora, and Podopsis, 



Although multivalve, we should approximate the 



ANOMIA, Bruguieres, 



To the Ostrese. The Anomiec 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 Ostreae. The greater part of the central muscle 

 traverses 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, Poli, has a small vestige of a foot, similar to that of a Pecten, 

 which slips between the emargination 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, like the Ostrese. They are 

 found in every sea. 



PLACUNA, Bruguieres. 



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

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



SPONDYLUS, Linnaeus. 



A rough and foliaceous shell like the Ostrese, 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 fossae 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, flattened, as if sawed 

 through behind the hinge. 



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

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



