516 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



waters with the other forms found associated with it, but that the speci- 

 mens may have been washed into the sea from streams on the neighbor- 

 ing shores. 



In several respects this species resembles Ccriiliium mexicanum, Gabb, 

 figured and described in the California geological report, from the Cre- 

 taceous rocks of Mexico. It differs, however, in showing, so far as yet 

 known, no traces of the varices seen on that shell; v/hile the little nodes 

 formed by the crossing of its revolving lines and vertical costse are trans- 

 versely elongated, instead of rounded, as on the Mexican species, which 

 is jjrobably a Geritkium. 



Locality and position. — Rock Spring, Wyoming, from a little above the 

 main ten-foot bed of coal at that locality. Bitter Creek series. 



Melania Goniobasis (?) WYOMiNGENSis, Meek. 



Shell attaining a rather large size, subterete, or very elongate-conical ; 

 volutions about nine or ten, the upper ones flattened-convex, and the 

 lower two or three more prominent; suture well defined but not deep. 

 Surface of upper volutions ornamented by small, regular, rather 

 crowded, and slightly arched vertical costse, crossed by five or six 

 regular revolving lines, that impart to them a granular or minutely 

 nodular appearance ; farther. down, the vertical costse become less and 

 less distinct, so as nearly or quite to disappear on the lower turns, 

 while tlie revolving lines become proportionally stronger, especially one 

 a little above the middle of each volution, which develops a revolving 

 row of rather distinct nodes that are compressed from above and below, 

 so as to become sharply prominent on the lower two volutions, thus 

 giving them an angular appearance; though the last one is rounded be- 

 low this angle. (Aperture unknown.) 



Length, 'about 2 inches; breadth, about 0.70 inch. 



It is not probable that this shell belongs properly either to the genus 

 Melania or 6o7iiobasis, as those genera are now restricted by the best 

 authorities in couchology ; though I have little doubt that it will fall 

 into Melania, as defined and understood by those who give greater lati- 

 tude to genera. It is probable that when its aperture can be seen, it 

 will be found to present characters that would warrant its separation 

 under a new generic name. I suspect, indeed, that some others of our 

 fossil-shells of this kind, from the fresh and brackish water-beds of the 

 Rocky Mountain region, will be found to belong to several undefined 

 groups; but until better specimens can be obtained, we can only range 

 them provisionally under the established genera to which they seem to 

 be most nearly allied. Undoubtedly at some future time specimens 

 will be found sufiicieutly well preserved to enable the paleontologist 

 to classify them more correctly. It seems desirable, however, in the 

 mean time, to define them, so that they can be used by geologists in 

 identifying strata, as it may be ages before perfect specimens can be 

 found ; while those we now have can be readily identified specifieally by 

 their ornamentation and other well-marked characters. 



Locality and position. — Black Butte Station, Union Pacific Railroad, 

 Wyo'.niug Territory. Upper beds Bitter Creek series. 



TERTIARY FORMS. 

 PiiYSA Beidg-eeensis, Meek. 



Shell attaining a large size, subovate in form; spire prominent, coni- 

 cal; volutions four and a half to five, moderately convex, last one large 



