104 PALiBOi^TOLOGY. 



anterior, rather broadly and regularly rounded in outline; base semi-ovate, 

 being more prominent behind, wliere it rounds up regularly into the poste- 

 rior margin, while it is somewhat straightened and sloping up gradually for- 

 ward; anterior end short, and truncated a little obliquely forward above 

 from the beaks to the anterior basal extremity, which i^ abruptly rounded 

 or subangular in outline ; hinge-margin straight, about half as long as the 

 shell, and rounding into the posterior margin behind, but not extending for- 

 ward beyond the beaks, which are slightly tumid, obtuse, depressed, and 

 located only about one-fifth the length of the shell from tlie anterior 

 extremity. Surface showing obscure lines of growth. (Hinge and anterior 

 unknown.) 



Length, 1.30 inches; height, 0.95 inch; convexity (of left valve only), 

 0.20 inch. 



Judging from external appearances only, this shell seems to be con- 

 generic with the last; but, as nothing is known of the nature of its hinge and 

 internal characters, I am equally in tlie dark in regard to its affinities. As 

 it resembles some of the forms included in the genera Modiomorpha, 

 I have referred it provisionally to that group, until its generic charac- 

 ters can be determined. It is a more convex shell than the last, and also 

 differs in having its anterior end obliquely truncated above, instead of be- 

 ing extended, rounded, and compressed in front of the beaks. 



Locality and position. — Same as last. 



GEPHALOPODA. 



OETHOOEEATITID^. 



Genus OETHOCERAS, Auct. 

 Obthoceras Blakei, Gabb?. 



Plate 10, fig. 11. 



Orthoceras Blakei, Gabb (1864), Geol. Survey of California. I (Palseont.), 19, fig. 1. 



The specimens here referred doubtfully to the above species consist 

 merely of two fragments, one of which seems to have belonged toward the 

 posterior part of the shell, though not showing the septa, and the other is a 

 part of the body-chamber. The first is gradually tapering, with a circular 



