96 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Some specimens collected at Horsetown that are possibly 

 referable to this species have a diameter of 15 centimeters 

 or more. 



Occurrence. — The type of this species was found in the 

 Horsetown beds a little to the east of Hulen Creek, Shasta 

 County, California. It is in the collections of the University 

 of California. 



39. Desmoceras subquadratum, sp. nov. 

 Plate IV, Fk;s. 118-119; Plate X, Fig. 193. 



Shell only moderately compressed; width of whorl nearly ecjual to depth; 

 umbilicus not so wide as in last species, ratio of whole diameter to umbilicus, 

 3.5:1; section of whorl subciuadrate; umbilical wall abrupt, broadly rounded 

 on the back; surface of the cast nearly smooth, showing none or only faint 

 constrictions; surface of shell marked by fine lines of growth and occasional 

 varex-like ridges that form the flexures commonly seen on the shells of this 

 group, bending more strongly forward in crossing the periphery; suture 

 characterized by stout lobes and saddles, lateral lobes four or five in number 

 on shells 7.5 cm. in diameter, decreasing uniformly in size toward the interior; 

 first lateral lobe nearly equally tripartite, the others less so; saddles nearly 

 equally bifid, with rounded terminations; width of shell increases with growth 

 more rapidly than the depth. 



This species is possibly one figured by Gabb in the Pale- 

 ontology of California (Vol. II, PI. XX) as Desmoceras 

 hoffmanni (Pal. Cal.,Vol. II, PI. XX). 



Occurrence. — This shell is not uncommon in the upper 

 portion of the Horsetown of Cottonwood Creek, Shasta 

 County, California, near the mouth of Hulen Creek. Four 

 of five good specimens were obtained at this place, some 

 of which are in the collections of the University of 

 California. 



The types of this and the preceding species, as here 

 described, are in the collections of the University of 

 California. 



40. Desmoceras colusaense, sp. nov. 



Plate V, Figs. 128-129; Plate X, Fig. 10a. 



In the collections of the State Mining Bureau in San 

 Francisco is a magnificent example of a Desmoceras of the 

 group D, flanulatiim^ nearly one foot in diameter. It is in 



