Geol— Vol. II.] ANDERSON— CRETACEOUS DEPOSITS. 8l 



Occurrence. — The specimen from which the figures have 

 been drawn is labeled " Mt. Diablo," and being in a collec- 

 tion with several others of the same species from Curry's 

 is probably also from that locality. Other species from this 

 locality, as stated elsewhere, show a low horizon of the 

 Chico. 



The type is in the collection of the University of California. 



19. Lytoceras rel. duvalianum d'Orh. 



Plate VI, Figs. 140-143. 



Ammonites duvalianus d'Orb., Pal. Franc. Terr., Vol. I, PI. L. 



Among the close allies to European forms found in the 

 Cretaceous of the Pacific Coast, there are few that seem 

 more truly identical than this one. If d'Orbigny's figure 

 represents the suture of this species correctly, both lobes 

 and saddles are relatively narrower in the California types, 

 otherwise there is but little difference, unless it is in the 

 less equal division of the lobes. The form of the shell 

 and its surface markings are too nearly like d'Orbigny's 

 species to justify any other name being applied at present. 

 There are certainly greater ranges of variation recognized 

 in nearly all Cahfornian types than there appear to be 

 between the specimens from California and the European 

 form as figured by d'Orbigny. 



In the young shell from the Shasta beds the constrictions are scarcely 

 noticeable but begin to appear upon the sides, without crossing the ventral 

 surface, at a diameter of 3 cm. They reach their clearest development at 4 

 or 5 cm., and then again diminish. At first they form upon the sides only 

 broad, undulatory ridges, between which the constrictions become more 

 sharply defined with growth, becoming deeper upon their posterior margin 

 and diminishing in depth forward. Between the constrictions, which are 

 about twenty in number, the surface is covered by fine transverse lines, yet 

 the shell has an almost polished appearance. The section of the whorl is 

 quadrate in the adult but is more rounded upon the ventral side in youth. 

 The walls of the umbilicus are abrupt, and the involution covers about one- 

 half of the width of the whorl. 



Occurrence. — Two good specimens of this species, one 

 of which is the type, were found near the mouth of Hulen 



