Geol.— Vol. II.] ANDERSON— CRETACEOUS DEPOSITS. 85 



result of Gabb's failure to recognize the true differences 

 in these forms. The various representatives of the species, 

 as understood by Gabb, for the most part may be easily 

 separated into this and the two following types : Lytoceras 

 batesi Trask (s. s.), Proc. Cal. Acad. Sci., Vol. I (2d Ed.) 

 1855, p. 39; Pal. Cal., Vol. I, p. 67, pars., PI. XIII. 



The most striking difference between this species and the 

 next one is in the rate at which they increase in diameter 

 with growth. In Trask's original type this increase was 

 relatively slow. According to his description, at a diameter 

 of 14 cm. the width of the aperture measured 3 cm. Gabb's 

 figure^ was probably drawn from Trask's type specimen. 

 According to Trask, the section of the whorl is about cir- 

 cular ("convolutions nearly round "). Both these charac- 

 teristics were overlooked by Gabb, who included with it two 

 species very different in both these respects. 



Occurrence. — It is not easy to decide the exact range of 

 this species from the statements of Gabb. Evidently, 

 though, it is found well toward the bottom of the Horse- 

 town, and seems to have a wide stratigraphical range. 



25. Lytoceras argonautarum, sp. nov. 



Plate VII, Figs. 154-155. 



Ammonites batesi (pars.) Gabb, Pal. Cal., Vols. I and II, 1863. 



Shell discoidal, somewhat inflated, increasing rapidly in size; section of 

 whorls not quite circular, flattened slightly on sides and ventrum; umbilicus 

 deep, walls rapidly becoming steeper outwardly; involution slight, like that 

 of the preceding species; suture similar to that of Lytoceras batesi, but cor- 

 respondingly heavier and less regular; lateral lobes not equally bipartite, 

 small siphonal saddle lanceolate, with minute denticulations; surface orna- 

 mented with rounded, evenly spaced ridges, separated by wide, smooth, and 

 shallow grooves, and in this respect unlike L. batesi. 



The type from which the figure was drawn was obtained 

 by Dr. J. P. Smith, one and one-half miles east of Ono, 

 Shasta County, California. Its greatest diameter is 17.1 cm., 



iPal. CaL, Vol. I, PL XIII. 



(7) December 10, 1902. 



