CALLISTOCHITON. 271 



In the depressed mucro and internal coloring, as well as the nar- 

 row eaves, this species resembles C. decoratus Cpr. ; but the sculpture 

 is much stronger, and is not obsolete at the dorsal ridge of each 

 valve. The C. elenensis of Sowerby, a species which I have 

 not seen, seems to be similar, but judging from Sowerby's figure the 

 mucro of that species projects at the summit of the posterior slope, 

 which is far from being the case with the form before me. The form 

 described as elenensis by Carpenter differs in having a very wide 

 sinus, weaker sculpture, etc. It should be compared with Carpenter's 

 unfigured Ischnochiton expresses, a species not known to me autopt- 

 ically. 



The type is in the collection of the Academy. 



C. PULCHELLUS Gray. PI. 60, figs. 1-6. 



Shell oblong, rather depressed, the dorsal ridge subangular, side- 

 slopes convex. Of a soiled buff color, the girdle darker, ashen. 



Valves not beaked ; lateral areas raised, cut by a sulcus into two 

 prominent ribs, of which the posterior is wider, sculptured with low, 

 transversely elongated grains, serrating the sutures, the anterior rib 

 having less conspicuous grains. Central areas in the middle pitted 

 in diagonal series, the pattern becoming coarser on each side, then 

 changing into longitudinal fine ribletson the outer half of each side. 

 Anterior valve having 10 (or 12) strong rounded ribs, cut into low 

 transverse grains by superficial concentric impressed lines. Posterior 

 valve abruptly depressed at the mucro, which is behind the middle, the 

 forward area level, reticulated, the posterior area bearing 1 stout ribs ; 

 the posterior ones are strongly bent. 



Interior whitish ; sutural-plates rounded, separated by a wide 

 sinus, which is angular but hardly notched at the sides, and not per- 

 ceptibly laminate. Slits in head-valve 10, median valves 1, poste- 

 rior valve about 14 ; teeth thin but normal in front and median, 

 irregular in the posterior valve. Eaves narrow. 



Girdle narrow, densely imbricated with minute smooth, flattened 

 scales. 



Length 10, breadth 5 mill.; divergence 135. 



Arica, Chili (Hennah.) 



Chiton pulchellus GRAY, Spicilegia Zoologica, pt. 1, p. 6, t. 3, f. 9, 

 (July 1, 1828). REEVE, Conch. Icon., t. 23, f. 153 (? and perhaps t. 

 25, f. 168). Chiton (Callochiton) pulchellus MORCH, Mai. Blat. 

 vii, p. 176. C. bicostatus D'ORBIGNY, Voy. dans 1'Amer., Merid., p. 

 486, t. 81, figs. 7-9. 



