PLACENTICERATID®. : 197 
PLACENTICERAS GUADALUP&“ (Roemer). 
Pl. XXIX, figs. 1-4. 
Ammonites quadalupe Roemer, 1852, Kreideb. v. Texas, pl. 2. 
The best specimen I have seen has a diameter of about 145mm. Outer 
volution on gerontic living chamber about halfway to the aperture is 63 
mm. and transverse diameter 47 mm., the same volution opposite is 43 mm., 
the transverse being 34 mm., avoiding the tubercles. The umbilici are 
deeper, the umbilical zones being more rounded and the involution greater 
than in pseudosyrtale. The involution covers the inner volutions to the inner 
line of tubercles, whereas in pseudosyrtale these are not only completely 
uncovered but well inside of the line of involution, The venter is very 
broad, so that the second lines of tubercles are on its lateral anglés and the 
first lateral saddles and lobes are on the ventral aspect. The alternating 
ventral tubercles and the flat ventral zone between them are retained on the 
venter throughout the ephebic stage. The inner row consists of large 
acute spines, solid at the tips only, which are large nodes on the cast, at 
the start when the umbilicus is only 25 mm. in diameter. These recede 
outwardly with age, but remain more prominent than in pseudosyrtale at the 
same age and the inner ridges are also much larger. The aperture is 
partly preserved and is apparently at the end of the metagerontic substage, 
judging by the last sutures, which are not closely approximated, and by 
the aspect of the last tubercles. The margin of the aperture has a sinus 
near the line of involution and broad lateral crest, but beyond this it could 
not be seen. The venter is convex and elevated in the gerontic stage and 
had a ventral zone as described above. The volutions are stouter at all 
stages than in pseudosyrtale. Having broken open this specimen, it was 
ascertained, as I had expected, that the young is more compressed and 
slender than the outer volutions, although in most Ammonitinze the reverse 
of this is true. The rounded nepionic volutions were followed as in other 
“Mr. T. W. Stanton has courteously commented as follows upon this species: 
“The original spelling ‘guadalupee’ should be restored. The name of the river is ‘Guadalupe.’ 
The type locality should be given ‘Waterfall of the Guadalupe below New Braunfels’ where the only 
horizons represented are the top of the Austin limestone and the lower part of the Taylor beds. The 
specimens from San Carlos are from beds probably of about the same age in a formation to which Mr. 
Hill has given the local name San Carlos beds. The Fort Worth locality [alluding to the specimen 
with that locality in my collection] must be inaccurate, as there are no Upper Cretaceous beds within 
several miles of that place.”’ 
