577 
The species are as follows: “xiteloceras (Heteroceras) Cheyen- 
nense and angulatum. LExtteloceras (Ancyloceras) uncum, Meek, 
Invertebrate Paleontology, Pl. xxi, is probably a fragment of the 
gerontic stage of one of these. 
Exiteloceras (Ancyloceras) Jennyi, Whitfield, Paleontology of the 
Black Hills, P\. xvi, has also similar ornamentation, but the costze 
differ somewhat. ‘This form, if the drawing is correct, has a ten- 
dency to asymmetry and when older was probably helicoidal. 
Ancyloceras lineatus, Gabb, Paleontology of California, has also 
similar costa, form and tubercles, but this may be a fragment of 
Ptychoceras. 
I have also before me two fragments, one 20 mm. in transverse 
diameter by 19 mm. ventro-dorsally, the other 17 mm. transversely 
by 20 mm. ventro-dorsally, which have precisely the coste and 
tubercles of /xiteloceras angulatum, as figured by Meek, namely, 
very prominent, subacute single costz reaching completely round 
the whorl, each one having two tubercles on the venter with a slight 
depression on the prominent costation between them. ‘They are 
fragments of helicoceran whorls and the aspect is altogether dis- 
tinct from that of any form in other genera. Loc., Elm Fork, 
Dallas county, Texas. Mamites Fremonti, Marcou, Geology of 
LVorth America, p. 36, Pl. i, Fig. 3, is probably a gerontic stage of 
some species of this group. ‘The anagerontic substage in his figure 
has single costae without tubercles, but the metagerontic substage 
has the retroversal bend and every third costation has two ventral 
tubercles. All costz are single and prominent. 
E-xiteloceras (Helicoceras) pariense, White, U. S. Geol. Survey 
We roo) Vera, Wheeler, Pt. 1, Paz, Pl.xix, Fig: 2, is another 
species of this series which shows by the twist in the costations that 
it is probably in older stages helicoidal. 
Ptychoceratide. 
I use this family name here provisionally and only in order to 
make clearer the essential distinctions that seem to exist between 
the series represented by the genera, Sciponoceras, Ptychoceras and 
Diptychoceras and other series of genera described in this paper. 
The young, so far as known, have slight, smooth shells in the 
neanic stage, the ephebic stage has the lines of growth and coste 
inclined forwards in passing over the sides and venter and probably 
PROC. AMER. PHILOS. SOC. xxxII, 143. 3 U. PRINTED JULY 18, 1894. 
