ciiiTONm^. 469 



Sub-fam. CHITONIN^. 



Mantle simple, without any pores or tufts of spines on 

 the sides. 



This sub-family is naturally divided into those which 

 have the valves exposed, including.the first eleven genera, 

 and those in which the valves are more or less covered by 

 the mantle, comprising the last three genera. Dr. Gray 

 finds that the plate of insertion of the anterior and poste- 

 rior valves of the first section is divided into several 

 lobes, and that of the central valves into two lobes, while 

 in the second division the plate of insertion of all the 

 valves has a single notch on each side, and that of the 

 hinder valves a single notch on each side, with a concave 

 sinuosity below. 



Genus LOPHYRUS, Poli. 



Mantle covered with regularly-disposed, smooth, imbri- 

 cate, roundish, conspicuous scales. 



Shell with the valves external, transverse, broad ; the 

 hinder valve with the apex superior. 



Syn. Lophuviderma, Poli. Radsia, Gray. Gymno- 

 plax, Gray. Lophurus, Gray. 



Ex. L. squaraosus, Linnceiis, pi. 53, fig. ]. 



The margin of the plate of insertion of the valves is 

 divided into lobes more or less denticulated, and the pos- 

 terior valve is entire behind ; the mantle-margin is con- 

 spicuously tessellated with smooth, roundish scales. The 

 species, which are very numerous, are found in all parts of 

 the globe. 



