268 CALLISTOCHITON. 



Chiton elenensis SOWERBY, P. Z. S. 1832, p. 27. C. ellinensis 

 SOWB., Conchol. Illustr., p. 6, f. 69. Ischnochiton elenensis CPU., P. 

 Z. S. 1865, p. 275, Probably Chiton janeirensis var. f GRAY,Spicil. 

 Zool., not of Sowerby and Reeve. 



Sowerby's original description and figures given above. I have 

 not seen this species, and place it in Callistochiton with some doubt, 

 as its internal characters may demand for it a position in Ischno- 

 chiton. Haddon considers it very closely allied to C. decoratus Cpr. 

 Carpenter has identified with this species a Panama form collected 

 by Prof. C. B. Adams. He gives the following description of it : 



" Outside having the central areas decussated with about 20 

 parallel bars ; lateral areas having two strong, swollen, tuberculose 

 ribs. Interior having the sutural [posterior] margin reflexed, 

 tuberculate, with a small sinus ; insertion plates 1-slit, sinus very 

 broad. Front valve having 12 ribs, not very strong, and ten slits 

 within, the teeth acute, eaves narrow. Posterior valve having the 

 mucro subposterior, depressed ; the slope behind it expanded, con- 

 cave, with about 12 subobsolete ribs; inside with 9 slits, the teeth 

 short, eaves small, callous within. The central valves of this species 

 are normal ; but the posterior valve offers a transition toward Callo- 

 chiton L Callistochiton], the outside being concave posteriorly, the 

 insertion-teeth short, and the eaves callous. (Cpr. in P. Z. S.). 

 The sinus is unusually broad and shallow, the sutural laminae not 

 being marked off. (Cpr.} 



C. EXPRESSUS Carpenter. Unfigured. 



Shell similar to I. elenensis, but flesh-colored. Central areas hav- 

 ing 10 distant closely decussated bars ; dorsal ridge acute, lateral 

 areas having two very strong, narrow ribs with narrow tubercles ; 

 inside having the posterior margin flat, hardly tuberculose, hardly 

 sinuated ; sinus narrow, angulated at the jugum. Anterior valve 

 having 10 strong, narrow ribs; interior as in elenensis, but with 8 

 slits. Posterior valve having a flat posterior mucro, the slope 

 behind expanded, hardly concave, with about 7 very strong ribs ; 

 inside having about 7 slits, the eaves flat. 



" With a strong general resemblance to I. elenensis, the differences 

 in detail in the only two specimens examined, as above stated, 

 appear of specific importance. If only varietal, it is equally impor- 

 tant to notice how much change is tolerated by the habits of the 

 animal. It may be the shell called Chiton clathratus by Professor 



