204 PSEUDOCERATITES OF THE CRETACEOUS. 
dichotomous, on the outer part of the outer volution on the cast, but these 
have no perceptible middle row of tubercles in the ephebic stage. The 
venter increases in the gerontic stage from being 5 mm. wide between the 
lines of tubercles to 20 mm. on the first half of the outer volution, and this 
continues to grow broader and more convex until near the aperture, where 
there is an apparent diminution. As the venter broadens, the cost are 
brought to the edges of the venter and their terminations become enlarged 
into rows of nodes as the gerontic stage progresses, but disappear in the 
paragerontic substage as the’ venter broadens and the surface of this 
becomes smooth on the casts. 
The living chamber is somewhat less than one-half of a volution in 
length. It has very deep sinuses on the umbilical zones and prominent 
lateral crests. The form of the ventral margin was not seen. The 
umbilicus is deep, the internal volution visible, the umbilical shoulders are 
prominent, and the umbilical zones are steep and broad, as in other species 
of this genus, from a comparatively early age. 
The sutures are of the guadalupzan syrtale type and well separated, 
becoming approximated only in extreme age. There is only one change, 
however, of considerable interest in the gerontic stage due to the broaden- 
ing out of the venter. The ventral lobe does not broaden in the same 
proportion, and consequently in this stage the first pairs of saddles and 
finally first lateral lobes become included within the outer line of tubercles, 
thus becoming transferred to the venter, as in P. guadalupe.- Another 
specimen (No. 11975 a) from the same locality is more compressed, has 
somewhat less prominent tubercles, and not so deep umbilicus. In the 
interior of the type specimen the venter of the later part of neanic 
stage with shell on is exposed. This shows the usual compressed form 
of this stage in other species of this genus, the venter narrow, smooth, 
concave, as in Protengonoceras, aud the volution also resembling that of 
that species, but at this time it is of course more discoidal. The largest 
specimen of the more compressed variety reaches a diameter of 134 mm. 
through the base of a living chamber and when complete must have been 
considerably larger. 
Ihave separated newberryi from P. planum after some hesitation, because 
of the entire absence of the peculiar tuberculated zone of guadalupe on 
the broadened venter of the gerontic stage, the more obscure tubercula- 
tions, and the more compressed young. ‘The second row of nodes is more 
