DESCRIPTIONS OF SPECIES. 153 
ENGONOCERATID-. 
Shells apt to be involute. The venter is concave and is occupied for 
its entire breadth by a smooth zone. The sutures are variable in the different 
genera and approximate in some forms to those of Sphenodiscus. ‘There is 
a similar tendency in most of the species to have broad saddles with 
phylliform bases, which are either entire or bifid, while the lobes have 
narrow bases and are more or less expanded apicad and apt to have trifid 
terminations. The simplicity and shortness of the saddles and lobes is 
correlated with the tendency to produce a much larger number of 
inflections and great variability in the outlines in the same species and 
sometimes even on different sides of the same specimen. The ventral lobes 
are short, spreading apically, and have usually pointed short and entire 
siphonal saddles. 
PROTENGONOCERAS Hyatt. 
The ephebic form is compressed and involute, as in Engonoceras and 
Metengonoceras of the same subfamily group, and it is also similar to the 
neanic stages of Hngonoceras, Sphenodiscus, and Placenticeras. 
The shell is smooth, except in the gerontic stage, where folds appear. 
The venter is moderately broad and decidedly concave, bordered by sharp, 
smooth ridges. These are exactly the external characters of the young 
during neanic stages of the species of the different genera mentioned. 
The sutures have the same ventral lobes as in Engonoceras and 
Metengonoceras, and similar lateral sutures, but the saddles are very broad 
and short and the lobes have fewer marginals. 
Type, Prot. gabbi (Bohm), Whitney collection, in Museum of Com- 
parative Zoology. 
The septa follow internally the curvatures of the sutures, concave 
along the mesal plane and convex only on the areas on each side of the 
zone of involution. 
PROTENGONOCERAS GABBI (Bohm). 
Pl. XVII, figs. 16-20. 
Ammonites pedernalis Gabb, 1869, Pal. California, Vol. LH, pl. 35, figs. 1, 1a. 
Engonoceras gabbi Bohm, 1898, Zeitschr. Deutsch. geol. Gesell., Vol. L, p. 197. 
A east of one-half of a volution in Museum of Comparative Zoology 
from Professor Whitney shows ephebic stage. The whole diameter, partly 
