TOiXiciA. 473 



valves. The species are usually of rather a small size, 

 and are principally inhabitants of the shores of temperate 

 climates, being found in Greenland, Britain, the Mediter- 

 ranean, and Western America. 



Species of Leptochiton. 



albus, Linn. Mecliterraneus, Gray. 



arbutum, Reeve. Mertensii, Midd. 



asellus, Chem. Milleri, Gray. 



cancellatus, Leach. muscarius, Reeve. 



cinereus, Linn. muricatus, Tiles. 



cingillatus, Reeve. proprius, Reeve. 



Colliei, Gray. pusillus, Soir. 



crocinus, Reeve. pusio, Sow. 



exiguus, Sow. ruber, Linn. 



giganteus, Tiles. scrobiculatus, Midd. 



Ifevigatus, Flem. versicolor, A. Adams, 



lividus, Midd. virescens, Reeve. 

 lentiginosus, Sou\ 



Genus TONICIA, Gray. 



Mantle simple, horny, naked, smooth or glabrous. 



Shell with the valves external, transverse, broad ; the 

 hinder valve with the apex superior. 



Si/n. Tonichia, GraT/ (olim). 



Ex. T. elegans, Fremhley, pi. 53, fig. 5, 5, a. 



The laminae of insertion of the terminal valves are 

 many-lobed, and those of the middle bi-lobed. According 

 to Dr. Gray, the valves are similar, with regard to their 

 plates of insertion, to those of Chiton, and that of the 

 posterior valve is entire. The chief external peculiarit}-, 

 however, consists in the simplicity of the mantle-margin ; 



VOL. I. 3 p 



