ACANTHOPLEURA. 213 



Girdle smooth, broad, extending between the valves, and when 

 living marbled with vivid red, green and blue. 

 Length 62, breadth 37 mill. 



Valparaiso, Chili. 



Chiton disjunctus FREMBLY, Zool. Journ. iii, p. 203, suppl. pi. 17, 

 f. 5 (between Oct., 1826 and May, 1827). EEEVE, Conch. Icon. t. 

 4, f. 21. GOULD, U. S. Expl. Exped., Moll, and Sh., p. 329. 

 Fannyia " dispuncta " [err. typog.] GRAY, Guide, p. 185. Fannia 

 disjuncta CPR., MS. 



" The transitions between this species and the normal Tonicice are 

 so gradual, that it scarcely seems entitled to generic rank. The 

 valves are not much more covered than in T. truncata ; but instead 

 of the lateral sinuses being angular, they are gradually rounded, and 

 extended to the apices of the valves. The principal peculiarity is 

 in the flattening of the mucro ; the creature, having devoted itself to 

 lateral expansion, had no need to push its tail up into a hump. 

 The slits are as short as if the valves were fully exposed, only extend- 

 ing up one-third of the teeth in the anterior valve and one-half in 

 the others. Inside, however, the gums rise to the level of the slits, 

 so that, when seen from within, the shell appears perfectly normal. 

 According to Gould, E. E. Moll., p. 329, the girdle is "distinctly 

 cleft" behind. This is duly represented in the Atlas, f. 417. I 

 have not, however, been able to trace it in either of the specimens 

 examined. That in Dr. Gould's own cabinet, although in good con- 

 dition, shows no trace of it. Neither Frembly nor Gray allude to it. 



Genus XV. ACANTHOPLEURA Guilding. 



Acanthopleura GUILD., Zool. Journ. v, p. 28 (in part), -f Core- 

 phium GRAY, Maugeria GRAY, Francisia CPR. 



Valves exposed, beaked, generally lusterless or eroded ; provided 

 with eyes on the forward part of the lateral areas and the end 

 valves ; mucro posterior ; interior colored, the tegmentum broadly 

 inflexed at the posterior margin of each valve. Insertion-plates all 

 conspicuously pectinated outside, and directed forward. Girdle 

 thick, covered with small or large calcareous spines. 



History of the name Acanthopleura. Under Acanthopleura, 

 Guilding defined seven sections, naming a representative of each. 

 His scheme is here reproduced, the modern equivalents of the species 

 named being added in brackets : 



