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



constrictions, which run straight across the whorl, and 

 lack the sinuosity so characteristic of L. alamedensc. The 

 striae of growth also run straight across, parallel to the 

 constrictions. 



A striking characteristic of L. alamedense is the contrac- 

 tion of the chambers after the first whorl, causing a bulging 

 of the protoconch and part of the first coil. This is shown 

 in the cross-section, PI. XVII, fig. i, and especially in the 

 larvae on PI. XVI, figs. 7 and 8, 9 and 10. 



Horizon and I^ocality : — jLytoceras alamedense was found 

 by Dr. L. G. Yates on the Arroyo del Valle, eight miles 

 southeast of Livermore, Alameda county, California, in 

 calcareous sandstone thought to belong to the upper Horse- 

 town beds, the top of the Lower Cretaceous. Associated 

 with it are Phylloceras ono'ense Stanton, Lytoceras hatesi 

 Trask, Desinosceras hoff)iianni Gabb, Haploceras breweri 

 Gabb, Hoplites r emo nd f Gdihh, Hoplites nov. sp. off H. duf- 

 renoyi d'Orb. of the Gault of France, Baculites occidentalis 

 Gabb, and other species not quite so characteristic. The 

 writer has not visited the locality in person, and so cannot 

 vouch for the occurrence of all these species in the same 

 beds. Mr. E. B. Kimball of Haywards at the request of 

 the writer recently made an excursion to the locality, but 

 could find only beds with Baculites occidentalis and B. chic- 

 oensis. It seems to the writer to be likely that both horizons 

 are present in such close proximity that they were not dif- 

 ferentiated m collecting, or possibly the beds may be transi- 

 tional from Horsetown to Chico. 



Ontogeny. 



Phylembryonic stage. — The first stage in reach of the 

 paleontologist is the protoconch, representing the earliest 

 shell secreted by the shell gland. The class or phylum is 

 already recognizable, but it is not possible to do more than 

 compare this stage with the primitive cephalopod. What 

 that was is unknown, although Tentaculites has been thought 

 by some naturalists to be the radicle of the group. It is 

 purely arbitrary to assign the protoconch to the end of the 



