182 SYSTEMATIC ARRANGEMENT 



Central tooth of Callochiton Icevis linear, somewhat narrower in 

 the middle, cutting edge transverse, smoothish, convex ahove ; first 

 side one scarcely larger, like a broad turned claw ; second very large, 

 with a subclavate scape, hollowed on the outside, hook minute, 

 wide, three-toothed ; lateral teeth 5, irregular, trapezoid, sixth erect, 

 between the second and third, subtriangular ; upper margin widely 

 reflexed, striolated. 



5. ISCHNOCHITON. 



Margin covered with very small imbricate scales ; valves thin ; the 

 plates of insertion very thin, smooth-edged, of the central valves each 

 with a single notch ; posterior valve entire. Gills nearly as long as 

 the side of the foot. 



f Scales of the mantle transversely grooved. 



1. I. textilis. 



2. I. limaciformis, A. Adams, Gen. MolL t. 53. f. 3. West Indies. 



3. I. Magdaliensis. 



4. I. altus. Philippines. 



ft Scales of the mantle minute, granular. 



5. I. marginatus, Zool. Journ. v. t. 5. 



6. Leptochiton. 



Margin covered with granular scales, with a series of spines on the 

 edge ; valves rounded, thin ; the plates of insertion rudimentary, 

 without any notches either in the terminal or central valves ; the 

 hinder valve entire. Gill short, on the hinder part of the side of the 

 foot. 



1. L. cinereus. 



2. L. Cajetanus. 



3. L. asellus, A. Adams, Gen. Moll. t. 53. f. 4. 



Central tooth of Leptochiton cinereus elongated, base oval, neck 

 slender, cutting edge transverse, wider, smoothish, convex above ; first 



Fig. 98. — Teeth of Leptochiton cinereus. 



lateral somewhat larger, slightly hooked, furnished on each side with a 

 large rounded wing, in the dorsal cavity receiving the produced base 

 of the second largest tooth ; scape thick, notched outside ; hook black, 



