56 NON-MARINE FOSSIL MOLLUSGA. 



elliptical, angular at its distal end, rounded at its proximal end, and 

 terminating at the end of the columella in a distinct, narrow canal, 

 which is slightly bent to the left. Surface marked only by faint lines 

 of growth. 



Length, 7 millimeters; diameter of last volution, 3J millimeters. 



CEKIPHASIID-E. 



The Ceriphasiidse, or American Melanians, constitute an important 

 feature of the non-marine fossil molluscan faunas of North America, 

 especially in the Laramie aud Eocene fresh-water strata of the west. 

 We have yet no evidence of the existence of this family before the Lar- 

 amie period; but in view of its known abundance during that period, 

 and also during that of the Eocene, it may be safely assumed that the 

 origin of the family was at an earlier period. It is nevertheless true 

 that the forms of Goniobasis, which occur in the purely fresh-water 

 Eocene strata, somewhat more nearly resemble those which are regarded 

 as typical forms among living species than most of those of the Lar- 

 amie period do. This, however, may have little significance as regards 

 physical changes since the Laramie, because the Uniones of that period 

 are more characteristically like living Uniones than those of the Eocene 

 strata are. 



All except two or three of the fossil species that have been described 

 as belonging to the Ceriphasiidse have been referred to the genus Gonio- 

 basis Lea; but a part of them have been so referred with some doubt. 

 Among those concerning which no doubt of this kind has been expressed 

 by the respective authors who have described them, there may be rec- 

 ognized at least three somewhat distinct subordinate types perhaps 

 worthy to be called subgenera. 



Of these three types, Goniobasis cleburni White, 67. tenera Hall, and 

 G. nebrascensis Meek & Haydeu, may be regarded as representatives 

 respectively ; but I regard it as probable that the latter type is more 

 nearly related to Lioplax than to Goniobasis. 



The Bear Eiver Laramie strata not only furnish what are probably 

 the earliest known species of the Ceriphasiida?,,but they furnish most of 

 the known species, four in number, which may be referred to that pro- 

 posed section of Goniobasis of which G. cleburni is the type.* The other 

 three species are, respectively, G. chrysallis Meek, G. chrysalloidca White, 

 and G. macilenta White.t All four of them are figured on Plate 6. They 

 are found associated together in the Bear Eiver Laramie beds of South- 

 western Wyoming and the adjacent parts of Utah, and none of them 



"The species of this type bears some resemblance to Melanopsis, but none of them are 

 canaliculate at base in any degree. No examples of Melanopsis, except the one de- 

 scribed on page 55 of this article, are known in North America, either fossil or recent ; 

 if we except the species Conrad described as Balliopsis. 



tSee description and figures of these four species, together with other references, 

 An. Rep. U. S. Geol. Sur. Terr, for 1878, Part I, pp. 91-93, pi. 30, figs. 4, 5, 6, 7, aud 10. 



