36 GEOLOGICAL SURVEY OF THE TERRITORIES. 
formed in rows, one being near the outer and the other near the inner 
border of the side of the volution. Upon the outer volution of very large 
shells the stronger costz become still stronger, the intermediate ones 
comparatively less distinct, and the plain space at each side of the ca- 
rina becomes a narrow depression. Septa having complex sutures, show- 
ing one peripheral and two lateral lobes, besides the crenulations of the 
auxiliary series and the secondary lobe of the outer lateral cell; also two 
full lateral cells, one being large and double and the other small; pe- 
ripheral] lobe narrow, rudely wedge-shaped, the point being directed back- 
ward; first lateral cell broad, and made almost double by the presence 
of a secondary lobe at its middle; median or first lateral lobe large, but 
not so broad as the first lateral cell, including both its divisions; second 
lateral cell somewhat smaller than either of the divisions of the first lat- 
eral cell; second or inner lateral lobe smaller than second lateral cell, and 
seareely larger than the secondary lobe at the middle of the first lateral 
cell; third or inner lateral cell not distinct as such except upon the side 
adjacent to the second lateral lobe, its outer end being continuous with 
the auxiliary series, which consists of an irregular crenulated suture, 
extending not only to the next volution within, but also to the inner 
median line, the latter part of it, however, being covered by the em- 
braced periphery of the next volution within. 
The borders of both lobes and cells are studded with short branches, 
serations, and crenulations as shown in fig. 1 e, plate 15. The first lat- 
eral cell might with propriety be regarded as two separate cells, and its 
secondary lobe as a small primary one, but I have followed this method 
of their description, because it is the one adopted by Mr. Meek, the au- 
thor of the genus, in his description of species under it. The siphuncle 
is of ordinary size, and is placed at the base of the perip eral carina, 
having a part of its diameter projecting within the base of the carina, 
which it so weakens that the latter is usually broken off in the imbed- 
ding rock. 
This shell often reached a large size, some of the examples indicating 
a diameter of coil little if any less than twenty-five centimeters. 
Although Mr. Meek made this species the type of his genus Priono- 
cycius, he never either described or figured it. The identity of the speci- 
mens upon which this description is based, and a part of which are rep- 
sented by figures upon plate 15 is, however, unquestionable, because 
he placed them in my hands as his types before his death. The speci- 
mens are somewhat numerous, but none of them are in a very satisfac- 
tory condition of preservation. No attempt will now be made to discuss 
the relation of this type to other proposed genera of Ammonitide, the 
principal object being, so far as practicable, to illustrate all the forms 
among the collections of the survey that have hitherto been described 
but not figured. 
Position and locality.—Cretaceous strata; probably of the Colorado 
Group; Valley of Medicine Bow River, Wyoming. 
