MALLEUS. 527 



Miihlf. Hippochseta, Sangiov. Isogonum, Bolten. Perna, 

 Brug., not J dans. 



Ex. I. ephippiurn, Linnaeus, pi. 123, fig. 1, 1, a. 



These animals are usually found attached by their byssus 

 to rocks in rather deep water. They are inhabitants of 

 tropical seas only, being found in the East Indies, the Cape 

 de Verds, and Western America, Fossil species have been 

 detected in the Trias of Europe, Chili, and the United 

 States ; iu some of these the posterior side is greatly pro- 

 duced and wing-like. 



Species of Isognomon. 



alatus, Gmel. Janus, Cpr. 



argillaceus, Gould. norma, Bolt. 



avicularis, Lam. legurnen, Gmel. 



Chemnitzianus, D'Orb. marsupium, Lam. 



costellatus, Conr. nana, Gould. 



crenatus, Gould. nucleus, Lam. 



dentiferus, Krauss. perna, Linn. 



ephippiurn, Linn. torva, Gould. 



eremita, Gould. vulsella, Lam. 



Genus MALLEUS, Lamarck. 



Shell sub-equivalve, irregular, greatly elongated at the 

 base; beaks small, diverging, central. Hinge straight, 

 eared on each side, without teeth, with an elongated, coni- 

 cal cartilage-pit under the beaks ; ligament partly external, 

 short. 



8yn. Himantopoda, Schum. Tudes, Oken. 



Ex. M. vulgaris, Lamarck, pi. 123, fig. 2, 2, a. 



In this genus the pearly lining of the valves does not ex- 

 tend as far as the ventral margin in the adult ; the young 



