DESCBIPTIONS OF SPECIES. 361 



The affinities of the Colorado form with Derby's Brazilian species, Productun 

 cTmndlessi, are very close. 1 have compared my specimens with a small collection 

 from Itaituba, Brazil, and except for one particular the two types seem to be identi- 

 cal, and perhaps the form under discussion would better have been referred, as a 

 variety, to P. chandlessi than to McChesney's species. The difference referred to is 

 that the Brazilian form has the anterior areas of the shell nearly or quite smooth, the 

 striae becoming obsolete over the additions of later growth. P. infiatus also closely 

 resembles P. iolmiensis of d'Orbigny. The prolongation of the hinge line into 

 projecting, enrolled ears is not as marked as in that species. Another closely allied 

 form is P. cora var. mogoyoni of Marcou, and I look to see all three appear some day 

 in synonymy. There can be no doubt that they are at least intimately related. 



Locality and /lansoii.—S&n Juan region (stations 2209, 2213, 2233, 224 Y); lower 

 portion of the Hermosa formation. Crested Butte district (station 2313); Weber 

 limestone. Leadville district (stations 2250, 2253, 2254, 2257, 2259?, 2265, 2267, 

 2268, 2271, 2275, 2281); abundant in the lower portion of the Weber formation, rare 

 in the upper portion. Ouraj' (stations 2195, 2195a, 2195b); Hermosa formation 

 Grand River region, Glenwood Springs (station 2193a). 



Productus gallatinensis Girty. 



PI. Ill, figs. 4, 4a, 5, 6 to 6b, 7, 8, 8a. 

 1899. Productus gallatinensis. Girty, U. S. Geol. Surv., Mon., vol. 32, pt. 2, p. 533, pi. 68, figs, lla-lld, 

 la-lc. 

 Madison limestone: Yellowstone National Park. 



Ventral valve very convex, strongly enrolled longitudinally, especially toward 

 the beak, which is sometimes placed anterior to the posterior outline of the shell. 

 Anterior portion nearly vertical, and but slightly curved. The sides also are nearly 

 vertical, .slightly converging toward the vault, which is broad and flattened, some- 

 times with even a shallow, slightly perceptible sinus. The anterior view would thus 

 be subquadrate in outline. Hinge line as long as the shell in front, the ears being 

 small and quadrate. 



The shape of the dorsal valve is semicircular or subquadrate. It is nearly flat 

 over the visceral region, strongly geniculate peripherally, the margin being normal 

 to the flattened portion of the shell. Ears small, quadrate, marked ofl' by grooves 

 near the hinge line converging to the beak. Visceral area crossed by strong, fine, 

 concentric wrinkles. 



The surface is ornamented with fine, strong, rigid, radiating strife, which num- 

 ber 8 to 10 in the space of 5 mm. The visceral region of both valves is crossed for 

 some distance by fine, strong, concentric wrinkles, and in the ventral valve the outer 

 portions of the shell are furnished with a small number of spines which are propor- 

 tionately rather large, and sometimes assume, when sufficiently numerous, a moi-e or 

 less regular quincunx arrangement. 



