114 PALEONTOLOGY. 



the latter and the suture, in the vertical wall of the umbilicus, there are .two 

 other minute, apparently simple lobes. First lateral sinus (saddle) a little 

 wider than the siphonal, which it exceeds in length on its inner side, rounded 

 at the end, and slightly serrated on the margins ; second lateral sinus much 

 like the first, excepting that its outer side is the longer. The other sinuses 

 are very small, and apparently nearly simple. 



Greatest diameter of the largest specimen seen, 2.20 inches; convexity, 

 0.70 inch. Some of the specimens are proportionally more compressed. 



This is one of the most common species found in the Nevada St. Cas- 

 sian beds. It seems to vary considerably in form, as well as in surface- 

 marking; the majority of the specimens before me, however, are less com- 

 pressed, and more obtuse on the periphery, than the typical specimen figured 

 by Mr. Gabb. A few of the others, however, seem to agree more nearly 

 with his figure, while there are so many gradations between these and the 

 less compressed form that I am inclined to regard the whole as belonging 

 to one species. 



Mr. Gabb mentions seeing a specimen from near Star City, which he 

 supposed belonged to this species, that was nearly six inches in diameter, 

 and had a row of large nodes around the middle of the whorls. Adopting the 

 conclusion that this really belongs to the species under consideration, the 

 numerous specimens before me would seem to be all young shells, or the 

 inner volutions of large ones, as none of them are more than two and a half 

 inches in diameter, or show the large lateral nodes mentioned by Mr. Gabb. 

 It is true none of them are entirely complete; but if the shell had ever 

 attained so large a size as six inches in diameter at the locality where our 

 specimens were obtained, there would probably have been some fragments 

 of these large individuals brought in with the others. 



As remarked by Mr. Gabb, this shell (that is the variety figured by 

 him) resembles Ammonites, or more properly, I should think, Ceratites sca- 

 pJiitiformis of Hauer; but it has the peripheral ridge decidedly less prominent, 

 and shows differences in the nature of the costse, and particularly in the 

 septa; which latter, in Professor Hauer's species, seem to me to present more 

 nearly the characters of Ceratites. 



The foregoing description and remarks were written out by me entirely 



