356 bulletin: museum of comparative zoology, 



(Gray) Pilsbrj, from Peru, but differing in the following particulars: the posterior 

 ribs of the middle valves are transversely striate, not nodular, and do not serrate 

 the suture ; the anterior valve has thirteen rounded finely cross-striated ribs, the 

 posterior has seven ; this valve considerably overhangs the posterior part of the 

 girdle, and the two anterior ribs are conspicuously larger and stronger than 

 the five between them. The gills are prolonged, reaching the second valve. 



Perico Island, Panama Bay, collected on the reefs by the " Albatross " party. 

 U. S. N. Mus. 110,763. 



CHITON LiNNt. 



Chiton (Chiton), sp. indet. 



A small species of the restricted group of true chitons was obtained at Tabo- 

 guilla Island, Panama Bay. It cannot be identified with any of the known species 

 from this locality, but the specimens may prove to be immature, and therefore it 

 seems best to leave it for the present anonymous. 



SCHNOCHITON Gray. 



LEPIDOZONA PiLSBEY. 

 Ischnochiton ophioderma Dall, n. sp. 



Shell blackish or brown with blackish, usually on the central areas longitudi- 

 nally disposed flecks ; interior dark bluish green, with an olivaceous flush under 

 the mucroues ; anterior and posterior valves each with ten rather deep, sharply de- 

 fined, narrow slits j middle valves with one slit on each side ; girdle with numerous 

 large, ovate, close-set, imbricated convex scales, smaller toward the periphery; 

 sutural plates large, the sinus indistinct; sculpture of the central areas minutely 

 quincuacially reticulate, but to the naked eye smooth; at the margin of the 

 lateral areas the lines become stronger, forming as it were a narrow sculptured 

 fringe just in front of the lateral areas; the latter, as well as the whole of the 

 anterior plate and the posterior area of the posterior plate, are covered with 

 rounded close-set low projections resembling scales ; there are no radial ribs or 

 ridges on any of the valves. Lon. of shell, 12; lat., 9; alt. of median ridge, about 

 2 mm. 



On the shore at Perico Island, Panama Bay. U. S. N. Mus. 110,764. 



The sculpture of this shell is quite remarkable. I do not remember seeing 

 anything like it in any otiicr Chiton. 



Tills and a few other species were obtained on the reefs or near the shore 

 by the "Albatross" party. 



