232 



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

 Is. is more satisfactory. 



This species is closely allied to A. borbonica 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 LIOLOPHURIN^E. 



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 a low 

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

 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 

 esj>ecially 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 Lorica volvox and L. angasi. All of the genera of 

 >nidce t Chiton, Eudoxochiton, Tonicia and Acanthopleitra, 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 jugosus (p. 178), Eudoxochiton 

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

 all showing more or less posterior emargination ; Acanthopleura 

 grnnii/nfu 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 Schizochitou and Lorica, the latter 

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

 probable that deposits not older than Miocene will furnish the 

 generic links now missing between the series of forms here included 

 tnd those grouped in L ilo/> h //////</. 



It is a notable fa<-t that the generic groups of Toniriitur and 



' MMMII 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: 



