48 CALLOCHITON. 



open on each side through a small rounded papilla in the vicinity 

 of the third or fourth branchia, counting forward, and between the 

 line of the gill row and the side of the foot. (DalL~) 



Genus X. CALLOCHITON Gray, 1847. 



Callochiton GRAY, P. Z. 6. 1847, pp. 126, 168; type Ch. Icevis. 

 SHUTTLEW Bern. Mittheil., Juni, 1853, p. 65. Callochiton GRAY, 

 Guide Syst. Dist. Moll. B. M. p. 181, 1856. Callochiton CARPEN- 

 TER MS. 1871, and of BALL, Proc. U. S. Nat. Mus. 1882, p. 286, 

 not Callochiton of Carpenter's earlier writings (P. Z. S. 1865, p. 

 276, etc.), = Callistochiton. 



Valves exposed ; insertion plates rising out of porous or spongy 

 eaves and cut into numerous teeth ; sutural plates connected or 

 continuous across the shallow jugal sinus. 



Two subgenera are recognized by Carpenter: 



Subgenus CALLOCHITON (restricted). 



Girdle covered with a smooth, compact layer of very small dia- 

 mond-shaped scales. 



Subgenus STEREOCHITON Cpr. 



Girdle leathery, more or less downy, frequently naked when the 

 delicate scales are rubbed off. 



Subgenus CALLOCHITON s. sir. 



The essential characters of the restricted genus Callochiton are 

 correctly stated by Carpenter as follows: (1) The insertion plates 

 are broken up into very numerous teeth rising out of spongy eaves; 

 (2) that these have a tendency to become propped outside; (3) that 

 the sinus is a mere wave in the otherwise united branches of the 

 sutural laminae ; (4) that the mantle is reticulated with what look 

 like diamond-shaped scales, which are only the points of long, flat- 

 tened, closely appressed corneous bodies, not found on any other 

 Chiton. For Gray's second group, in which the peculiar covering 

 is not seen, a subgenus should be created, unless indeed the species 

 may rank under Trachyradsia. For two species with a mantle 

 intermediate between Choetopleura and Tonicella I have established 

 a subgenus Stereochiton. Of the whole series there are very few 

 species known. All of them are rare and display very little sculp- 

 ture on the valves. 



