174 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bull. 106. 



Genus PBIONOTKOPIS Meek. 



Prionotropis woolgari Mantell (sp.). 



PI. XLii, Figs. 1-4.. 



Ammonites woolgari Mantell, 1822, Geol. of Sussex, p. 197, PI. 22, Figs. 6 and 7; Sow- 

 erby, 1829, Min. Conch., vi, p. 25, PI. 587, Fig. 1; Sharpe, 1853, Fossil Remains 

 Moll. Chalk of England, p. 27, PI. 2, Figs. 1 and 2, and various other European 

 authors; Meek and Hayden, 1861, Proc. Acad. Nat. Sci. Phila.,p. 421. 



Prionocyclus (Prionotropis) woolgari Meek, 1876, U. S. Geol. Sur. Terr., vol. ix, p. 455, 

 PI. 7, Figs, la-h and PI. 6, Fig. 2. 



Not Ammonites woolgari d'Orb. Paleont. Franc Terr. Cre"t., vol. I, PI. 108, Figs. 1-3. 



Ammonites percarinatus, Hall and Meek, 1856, Mem. Am. Acad. Arts and Sci., 2d ser v 

 vol. V, p. 396, PI. 4, Fig. 2. 



Compare A. bravaisianus and A. carolinus d'Orb., op. cit v PI. 91. 



Meek's description is as follows : 



" Shell attaining a medium size, more or less coinpressed-discoidal, 

 the outer turn being proportionally more convex (including nodes) than 

 those within; umbilicus about equaling the greatest dorso- ventral 

 diameter of the last turn; each volution embracing about one- fifth of 

 the next within, and having its umbilical margin slightly indented by 

 the uncovered nodes forming the inner of the two outer rows on the 

 succeeding volution within. Young examples, half an inch to one inch 

 in diameter, with costa3 linear, closely arranged, of nearly uniform size, 

 and manifesting scarcely any tendency to develop nodes, but already 

 showing the forward curve of their outer ends well defined, while the 

 peripheral keel is low, narrow, and simple, and the furrow on each side 

 shallow. At a somewhat larger size, costa3 usually more or less unequal 

 in size, the larger ones now beginning to develop the two nodes at their 

 outer curved ends, and to become a little more prominent and compressed 

 at their inner extremities, while the rather more prominent keel begins 

 to develop its eremite outline, and the nodes nearest it to assume their 

 compressed form and parallel arrangement. On attaining to 2£ to 3 

 inches in diameter, costse, nodes, and keel becoming more prominent, 

 the latter being strongly compressed and deeply and largely scal- 

 loped, with divisions rounded in outline ; while at this stage of growth, 

 the periphery, as seen in profile, would seem to be very deeply sulcated 

 on each side of the keel, but this is due to the prominence of the row 

 of nodes on either side of the same. Costa? , when the shell has at- 

 tained a diameter of 4 inches, much depressed in the middle, with 

 the nodes at their inner ends thicker and more obtuse, and those near- 

 est the keel more depressed or nearly obsolete, while those of the third 

 series, near by, become much enlarged and produced obliquely out- 

 ward as short, thick, spine-like projections. Soon the outer compressed 

 nodes disappear, and the keel is only represented by distinctly sepa- 

 rated, low, elongated nodes; and when the shell has attained a diame- 

 ter of 7 inches, the costae are more distant, greatly elevated, com- 

 pressed, and almost wing-like, but still retain a large, prominent, sub- 



