PLACENTICERATID 2. 203 
pressed. There are small tubercles in the umbilicus but these disappear in 
the older stages, and almost the entire outer volution is smooth. The other 
specimen has similar characters, and the sutures are of the guadalupe and 
syrtale type. 
This species is not separable in some varieties from P. newberryi, except 
by the absence of large lateral nodes at all stages. 
Locality: San Carlos, Presidio County, Tex.; Presidio del Norte, 
Mexico. 
Age: San Carlos beds, Upper Cretaceous. 
PLACENTICERAS NEWBERRYI 0h. sp. Hyatt. 
Pl. XXXI, figs. 3-5. 
The type is a cast with small patches of shell. Diameter is 120 mm., 
to which must be added perhaps 5 mm. for depression of outer volution. 
The diameter of the whole coil one-fourth of a volution younger and not. 
altered by depression is 94 mm. The outer volution at aperture is 54 mm. 
and transverse is 39 mm., the umbilicus is 24 mm. and the opposite part of 
same volution is 42 mm. and transverse 28 mm. The last volution begins 
with transverse diameter of 19 mm., enlarges in the next quarter of a 
volution to 28 mm., and just beyond this the large gerontic tubercles begin. 
The transverse diameter continues to increase until the last quarter apicad 
of the aperture is reached, and then it diminishes between the two last 
tubercles, which are widely separated, and still further diminution takes place 
at the aperture. In another specimen there is no diminution in the rate of 
growth of the transverse diameter apparent to the eye, but this specimen 
has not a complete living chamber. The almost scaphitean aspect of the 
living chamber in scme specimens is misleading and is in part due to 
depression. Nevertheless, this only exaggerates the gerontic metamorphoses 
of this interesting species. Small nodes are present in an early ephebic 
substage on the umbilical shoulders and continue to increase, becoming 
very large suddenly in the anagerontic substage. Elongated tubercles are 
present on either side of the venter in the ephebic stage, but the age of 
introduction was not ascertained; apparently it is later than that of the 
tubercles on the umbilical shoulders. 
The latter are widely separated at all stages, but the ventral tubercles 
are close together. There are very obscure fold-like costz, some of them 
