136 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 30 Ser. 



Genus Lytoceras Suess. 



Lytoceras in the strictest sense comprises species with wide, shallow, 

 umbilicus, whorls little embracing, and shell rather smooth except for fine 

 ribs made up largely of the striae of growth, and occasional varices and con- 

 strictions ; they have a divided siphonal lobe, two lateral and one auxiliary 

 lobe. 



It ranges from the Lias to the Upper Cretaceous. Ac- 

 cording to Steinmann ^ Lytoceras is probably descended 

 froin Monophyllites, classed by many naturalists with the 

 Phylloceratidas. Zittel'-^ in his latest work considers the 

 Lytoceratidas as direct descendants of the Prolecanitidae, 

 and therefore not from Mojwphyllites, which he assigns to 

 the Cyclolobidse. E. von Mojsisovics '"^ says that Lytoceras 

 sprang irova Alonophyl/ites s. str., and that Phylloceras C2ivaQ. 

 from Mojsvarites, a subgenus under that saine group. 



All that has been done on the ontogeny of this genus is 

 the work of Branco'*, who described and figured some of 

 the larval and adolescent stages of Lytoceras ger^naini but 

 did not give the complete development, nor compare these 

 stages with antecedent genera. On the same plate Branco 

 figures some larval stages of {Lytoceras^ simonyi Hauer, 

 but this species belongs to Monophyllites. Neumayr con- 

 sidered Tnrrilites, Baculites, and several other abnormal 

 ammonoids as derivatives from the Lytoceratidae; and 

 indeed the larv« of Baculites, as figured by Amos Brown ^, 

 do resemble very closely those of Lytoceras, as do also 

 those of certain Scaphites, according to unpublished obser- 

 vations of the writer. It is quite likely, however, that 

 Scaphites is not monophyletic. 



Lytoceras alamedense, sp. nov. 



Plates XVI-XVIII. 



This species is evolute, with wide, shallow umbilicus and coils that increase 

 very slowly in size, thus scarcely embracing the preceding. The shell is 



1 Elemente d. Pal., 1890, p. 420. 



- Grundzuege d. Pal., 1895, p. 435. 



3 Denk. K. Akad. Wiss. Wien, Bd. LXIII, 1S96, p. 95. 



1 Palaeontographica, Vol. XXVI. Beitr. Entwick, Foss. Cephal., PI. VIII, fig. 6. 



■■' Proc. Acad. Nat. Sci. Phila., iSgi, p. 159, and 1892, p. 136. 



