JURASSIC FAUNA. 253 



CEPHALOPODA. 



Belemnltes paclficas, Gabb. Proc. Cal. Acad. Sci., Nov., 1864, p. 173. 



This species has never been figured from California, but one from 

 Alaska supposed to be identical with it has been described by C. A. 

 White* as associated with Aucella. In the slates at Texas ranch a few 

 specimens were found, but too imperfect to be satisfactorily identified. 

 Cardioceras altenians, von Buch. 

 Ammonites alternans, L. von Buch, Gesammelte Werke, vol. iv, p. 454, 



pi. 18, fig. 4. 

 Ammonites alternaaSj Quenstedt. Ammoniten des Schwabischen Jura, 

 p. 824, pi. 91, figs. 1-25. 



This species is a very variable one, and probabl}^ not all the varie- 

 ties united by Quenstedt are the same ; still this group of Cardioceras 

 is well marked and easily distinguished from that of C. cordatum, 

 Sowerby, and C. cordiforme, Meek and Hay den. This species diff'ers 

 from C. cordiforme, Meek and Hayden,t in having the sides less arched 

 and the involution less ; also on 0. cordiforme the ribs are more numer- 

 ous and usually each alternate rib forks at the umbilicus and swings 

 with a gentle curve forward, nowhere showing a tendency to produce 

 knots. In C. cdternans the ribs fork with great irregularity, sometimes 

 each alternate one and sometimes the third or fourth. They fork about 

 half way to the outside or ventral portion of the shell, forming usually 

 a small knot at the fork, and often forming a second one where the ribs 

 make their sickle-shaped bend forward on the external side. 



The very high, sharp, strougly serrated keel is characteristic of this 

 species. 



The specimens are all distorted from the crushing of the slates, and 

 thus are elliptical instead of spiral, but the}' show the same amount of 

 involution as that given on the figures of Quenstedt. The umbilicus is 

 much wider and less deep than that of C. cordiforme, Meek and Hayden, 

 or C. cordatum, Sow.erby. 



The body chaml)er is about one coil in length. 



A closely related species has been described ])y Pavlow X under the 

 name Cardioceras volgx, Pavlow, of the zone of Aspidoceras acanthicam, 

 lower Kimmeridge, but that species is much more involute than the 

 California specimens, while the fineness- of the costse is about the same. 



Cardioceras suhtilicostatam, Pavlow,§ is still more closely related to our 

 species, but is also more involute. It may be identical with a variety of 



* Bull. 4, U. S. Geol, Survey, p. 14, pi. vi, figs. 1:5, 14. 

 t Pivl. Upper Missouri, p. 122, pi. v, tig. 2. 

 X Mem. Com. Geol. (Russia), vol. ii, no. 4, p. 8*;, pi. viii, tig. 5. 

 • ^Op. eit., p. 80. 



