232 LIOLOPHURIN^E. 



never grew at those places. The evidence in favor of the Comoro 

 Is. is more satisfactory. 



This species is closely allied to A. borboniea in sculpture, but it 

 differs in having flatter, thinner valves, longer, white-tipped spines, 

 in lacking the white dorsal stripes as well as in the color of the inte- 

 rior. Finally, the characters of the tail insertion plate differ. 



Subfamily LIOLOPHURINJC. 



Median and anterior valves provided with eyes, and having well- 

 developed insertion-plates with slits, the teeth pectinated outside, not 

 thickened at the edges of the slits. Posterior valve with the mucro 

 posterior and terminal ; its insertion-plate obsolete, reduced to alow 

 ridge or flat ledge of callus, which is unslit (except in Schizoehiton) 

 and continuous posteriorly or interrupted in the middle by a caudal 

 sinus. Gills as long as the foot. 



This group is closely allied to Chitonidce and has doubtless been 

 derived from the Tonicioid branch of that stock. It is separated 

 from them on account of the degeneration of the posterior valve and 

 especially its insertion-plate, a character of vastly less importance 

 than Carpenter supposed. The median notching of the tail valve 

 behind is also extremely variable, as is exemplified by such closely 

 allied forms as Loriea volvox and L. angasi. All of the genera of 

 Chitonidce, Chiton, Eudoxochiton, Tonicia and Acanthopleura, show 

 species in which the tail valve has an incipient caudal sinus, or in 

 which the insertion-plate is becoming obsolete, or both conditions. It 

 is only necessary to mention Chiton jug osus (p. 178), Eudoxochiton 

 (pp. 193, 194), Tonicia confossa (p. 210); Acanthopleura spinigera, 

 all showing more or less posterior emargination ; Acanthopleura 

 granulata and the section Amphitomura have the posterior insertion- 

 plate very short, some forms of the latter having it nearly deprived 

 of slits. Compare with these Schizochiton and Lorica, the latter 

 having the insertion-plate short but distinctly crenulated. It is 

 probable that deposits not older than Miocene will furnish the 

 generic links now missing between the series of forms here included 

 in Toniciince and those grouped in Liolophurince. 



It is a notable fact that the generic groups of Toniciince and Lio- 

 lophurince seem to mutually correspond to one another, as though 

 the several generic stocks of the former subfamily had been simul- 

 taneously modified in the same manner, thus : 



