DESCRIPTIONS OF SPECIES. 363 



generallj' been considered a synonj^m of Prodiictiw costatus Sowerby. The identi- 

 fication of American forms with Sowerby's species has often been made with protests 

 and reservations on the part of authors, and in most cases can be justified onlj^ by 

 allowing- very broad specific limits to the European form. Meek" clearly doubts 

 the correctness of his identification of Nebraska specimens, and quotes Davidson to 

 the effect that the American forms referred to P. costatus are in fact more closely 

 allied to P. semireticiilaf'u^. With this I am ready to concur, and the widelj' distrib- 

 uted shell identified with that species as a variety in Colorado is perhaps more 

 nearly in agreement with P. costatus. as identified by American paleontologi-sts, than 

 with the form commonly referred to P. semireticulatus. P. portlockiamis comes 

 closer to true P. costatus than the form which gave rise to the comments of Meek 

 just mentioned, but I think it can not be strictly referred to Sowerby's species. 

 1 therefore propose to revive Norwood and Pratten's name for the form. 



Locality and horizon. — Dolores River region, Sinljads Valley (station 2285); 

 top of the Hermosa formation. 



Produgtus sp. h. 



PI. Ill, figs. 9-9b, 10, 11. 



This form has been found at but two localities. Eight specimens from a station 

 in the San Juan region, and a few poorl}' preserved and doubtfullj^ determined 

 examples from another in the Leadville region, constitute all the available material, 

 which is insufiicient to disclose completely the specific characters of the tj'pe to which 

 it belongs. For this reason and because* in shape and other general characters it 

 resembles a group of Producti already sufiiciently described, viz, P. semireticulatus 

 var hermosanus, P. inflattis. P. (/aJhitinensis, and JUarginiJ'era, no formal description 

 will here be given. 



Productus sp. h most resembles, perhaps, the Colorado form of P. inflatus. It 

 is distinguished l)y its smaller .size, being only about 30 mm. across the hinge line, 

 and by the fact that the ventral valve is narrower and more rounded, and without 

 the mesial sinus which mai'ks the larger shell. The surface ornamentation seems to 

 be about the same. Productus sp. h resembles the form from Sneedville, Tenn., 

 which has also been referred to P. inflatus. The latter, as already noticed, is 

 smaller than the Nebraska type of McChesney's species and much smaller than the 

 Colorado representative. Productvs sp. h, however, has considerably finer strise and 

 is without a mesial sinus so far as observed. 



In size and shape dorsal valves are closely similar to the dorsal valve which I 

 have identified as Marginifera lasallensis, Init the striation is much finer. It also 

 resembles P. gallatinemis, but is larger and stands midway between that species 

 and P. inflatus. 



a r. S. Geol. Siirv. Nebraska, 1S7^;, pp. im. 160. 



