360 CAEBONIFEROUS FORMATIONS AND FAUNAS OF COLORADO. 



Beak small, incurved, projecting but slightly beyond the hinge line. Ears rather 

 large, extended, vaulted. Sinus broad and shallow, distinct though not strong. 



Dorsal valve slightlj^ concave over the visceral portion. After attaining a length 

 of about 20 nun. the curvature is strong and sudden, and subsequent growth follows 

 that of the other valve. The visceral cavity is of considerable height, sometimes as 

 much as 1.5 mm. , but usually a little less. 



The surface is marked by numerous fine, even, wire-like, radiating strife, and 

 posteriorly, over about one-third its length, by concentric wrinkles. The spines are 

 few and distant, though large. They are scattered over the surface, sometimes in 

 more or less regular quincunx arrangement. Often one or two of the striss are 

 interrupted by each spine as it develops, to reappear in a bifurcated condition, three 

 or four originating at each spine base. 



This form closely resembles the one which I have designated as Produci/us senii- 

 reticyiilatus var. hermosa/nus. 1 am unable to point out any differences of significance 

 in the conformation of the shell, and the chief distinction concerns the surface orna- 

 mentation. In the more tj^pical examples of Productus inflatus the concentric 

 wrinkles and radiating strife are much finer and the spines smaller and more numer- 

 ous. As many as 15 or 16 stride occur in the space of 10 mm., while in Prod^cctus 

 semireticulatus var. hermosaims onlj' 9 or 10 are found in the same distance. Varia- 

 tion from this proportion in P. injlattis, however, is rather toward coarseness than 

 fineness, and the two forms intergrade so that, while well-characterized examples can 

 be readily distinguished, others are found which it is difiicult to discriminate, identi- 

 fication with one species seeming to present equal claims with the other. 



Productus infiatus is certainly a good variety of P. semireticxdatus vtir. hermo- 

 sanus, but I doubt if it should be accorded higher recognition unless on account of 

 the difference in I'ange which our Colorado collections indicate. 



This form occurs also in the Mississippi Valley, and I have identified it at liock 

 Bluff, Nebr. , Bellevue, Nebr. , and at Sumner, Kans. A form which is probabljr the 

 same is found also at Sneedville, Tenn., and li miles east of Cumberland Gap, Tenn. 

 The fossils from Colorado are somewhat larger than those from Kansas and Nebraska, 

 while the Tennessee collection shows a still smaller and somewhat more coarsely 

 striated variety. 



I am uncertain as to the correct identification of this species. The form from 

 Colorado and that from the localities in Kansas and Nebraska just mentioned are, I 

 have little doubt, the same. Except for being a trifle larger, this type answers 

 closely to McChesney's description of Productus inflafus, but this author fails to give 

 exact data regarding the size of the strife in the form he was describing. The shell 

 from Sneedville is possibly more typical than that from beyond the Mississippi. As 

 I have alread}^ stated, it is smaller and somewhat more coarsely striate, and I am not 

 satisfied that it is conspecitic with the latter. 



