IJolophnrin;.-. 

 H disposed in radiat.ing hands;! 



valves polished and bright colored 



n ... . ,, > Ontthochiton. 



outside, ponvllanous \vitlnn; girdle 



[leathery, nude. 



f Eyes scattered among the tubercles! 



of the surface, which is rough and 



Maugtna < . . ' . ' . .. } Liolophura. 



lusterless ; interior dark ; girdle 



[clothed with calcareous spines. 



(Eyes very minute, oval, scattered;! 

 surface of valves brown and polished I 7 , . 

 ,. > Enoplochiton. 

 outside when not eroded, peculiarly 

 sculptured inside. 



The genera Lorica and Schizochiton have no representatives in the 

 Toniciitice, for while they are closely allied to the latter, they have 

 been differentiated along a line away from that taken by Onitho- 

 chiton and its immediate allies. 



Synopsis of Genera. 



A. Median valves having eyes developed only on the diagonal ribs. 

 Sinn* notably narrow and small. Insertion-plate of tail valve a low, 

 rounded, rugose ridge more or less notched or waved upward in the 

 middle behind, or sharp, long and pectinated. 



B. Eyes large, situated on the diagonal ribs and on the ribs of the 

 head valve, the latter corresponding to slits in the insertion-plate. 

 Girdle having minute calcareous spines. 



Genus XVI. SCHIZOCHITON Gray. 



Much elongated. Posterior valve having a deep caudal sinus 

 with one or two notches on each side of it in the insertion-plate. 

 Head valve with few (about 6) slits. Girdle sparsely, finely spinulose, 

 slit behind. 



BB. Eyes reduced to minute, fuuctionless punctures on the summit 

 of the diagonal ribs, and entirely absent on the head valve, the riblets 

 of the latter not corresponding to internal slits. Qifdfa dfnseli/ s<'ah/. 



Genus XVII. LORICA H. & A. Adams. 



Oval or ovate, elevated. Posterior valve having a deep caudal sinus 

 or a shallow wave, the insertion-ridge otherwise uninterrupted. 



