316 GEOLOGICAL SURVEY OF THE TERRITORIES. 



to Deshayes' section " oblongues transverses " of Cyrena, wliicli in- 

 cludes some very thin species from the Paris Basin. 



It is a curious fact, that at the same time these forms differ so very 

 materially in form from the existing typical species of Corbicula, they 

 have the lateral teeth of the hinge, in most cases, like those of that 

 group, often even to the fine transverse striae, instead of like those of 

 the true Cyrenas. As Deshayes has remarked, the fossil species show 

 gradations in form and hinge characters, that seem to indicate that 

 those groups can scarcely be regarded as forming distinct genera, al- 

 though it may be convenient to distinguish them subgeuerically. There 

 would still, however, apparently be as good reasons for forming for 

 these longitudinally-ovate or subtrigonal, very thin shells, with hinge 

 teeth- more like those of Corbicula, a third subgeneric section. If so, I 

 would propose for this group the name Leptesthes, with the first of the 

 foregoing species as its type. 



Locality and position : Same as last. 



GONIOBASIS CHYSALLIS, (MEEK.) 



Shell generally almost cylindrical below the middle, but more abruptly 

 tapering above; volutions six or seven, flattened, with the upper margin 

 thickened, last one not angular, and scarcely larger than the next above 

 it; suture well defined. Surface ornamented by distinct vertical costae, 

 often ranging nearly in the same line all the way up the spire; these are 

 partly interrupted by an effort to form three, or rarely four, obscure re- 

 volving lines or ridges, the upper of which is larger and more prominent 

 than the others, which character, with the slightly enlarged upper ends 

 of the vertical costae, causes the thickened appearance of the upper mar- 

 gins of the volutions ; several other slender and more distinct revolving 

 lines also occur on the under side of the last turn. Aperture somewhat 

 rhombic-ovate. 



Length, about .60 inch ; breadth, .18 inch. 



I have seen no well-preserved specimens of this shell, but its peculiar 

 form and the thickened character of the upper margins of its volutions 

 distinguish it readily, even in very imperfect examples, from all of the 

 other known species of this region. I had long back referred it, with 

 much doubt, to Goniobasis tenera, Hall, (sp.,) (not Anthony;) but as the 

 later collections brought from Utah and Wyoming contain a great 

 number of another, but clearly distinct species, that agrees more nearly 

 with Professor Hall's figure, both in form and the number of revolving 

 lines ou each volution, I am led to think that he must have had the 

 latter species before him when he described his G. tenera. The fact, too, 

 that it occurs in vastly greater numbers than the form under consid- 

 eration, seems to sustain this conclusion. 



Locality and positien : Bear Biver, near Sulphur Creek, Utah ; Lower 

 tertiary. 



GONIOBASIS NODULIFERA, (MEEK.) 



Ceritliium nodidosum, Hall, 1845. Fr6mont's Roport Explorations, p. 309, PI. Ill, Figs, 

 11 and 12. (Not Goniobasis nodulosa, Lea, 1841.) 



Shell attaining a rather large size, elongate-conical ; spire much pro- 

 duced ; volutions seven or eight, convex, and increasing gradually and 

 regularly in size ; last one not larger in proportion than the others, and 

 rounded ; suture well defined and sometimes presenting a slightly banded 

 appearance ; aperture ovate ; outer lip very strongly sinuous above the 

 middle, and prominent below it. Surface ornamented with rather dis- 



