ISCHNOCHITON. 53 



Conch. Icon., t. 5, f. 25. NOT C. castaneus Quoy nor C. castaneus 

 Conth. O.cerasinus Chemn., REEVE, Conch. Icon. f. 63. 



This species is variable in coloring, being either uniform chestnut 

 brown or having spots and patches of brown on a lighter ground. 

 The interior is always roseate. The numerous narrow teeth, short 

 spongy eaves, spongy slits, etc., readily separate it from other forms. 



C. LOBATUS Carpenter, n. sp. PL 8, figs. 83-85. 



Shell large, flattened, with acute jugum ; intense olive colored; 

 umbo median, the posterior slope concave. Valves scarcely beaked, 

 rounded at the margins. Lateral areas not well defined. Entire 

 surface minutely granulated in quincunx. 



Interior : Posterior valve with 20, median valves 5 to 7 (usually 

 6, the posterior minute), anterior valve 24 slits. Teeth small, 

 deeply separated, and outside very strongly propped, as if bilobed ; 

 interstices deeply spongy. Eaves small, spongy, grooved inside ; 

 sinus subobsolete ; sutural plates connected. Girdle leathery, 

 smooth, under a lens seen to bear short, minute, sparsely placed 

 hairlets. Length 41, breadth 27 mill.; divergence 130. 



Tasmania. (Mus. Cum. No 19.) 



This fine and curious species has the general aspect of Mopalia 

 vespertina (from which it is known at once by the lophyroid 

 mucro) ; the insertion plates, props, spongy eaves and minute sinus 

 of Callochitou ; and a mantle resembling an aberrant Tonicia. 



Genus XL ISCHNOCHITON Gray, 1847. 



=Ischnochiton -f Trachydermon + Maugerella Cpr. 



Valves external, having sharp, slit, insertion plates, the teeth not 

 buttressed. Eaves solid (rarely somewhat porous in s. g. Trachy- 

 dermon} ; girdle covered with imbricating scales, either flat or con- 

 vex, smooth or striated. Gills typically extending the entire length 

 of the foot, but in some species they are short in front or at both 

 ends. 



Ischnochiton is the typical or central point in development of the 

 sharp-toothed division of Chitons, around which the other genera 

 naturally group themselves. 



The great diversity in the girdle covering permits us .to use that 

 character for the foundation of a number of subgeneric and sec- 

 tional divisions, as follows: 



