SPHENODISCID®. 59 
SPHENODISCUS PLEURISEPTA (Conrad). 
eee hos sy i allelic Verh ost Saab \VelestionnGs 
Ammonites pleurisepta Conrad, 1857, U. S. and Mex. Bound. Surv., Vol. I, Pt. I, 
p: 159, pl. 15, figs: 1, a, b, c. 
Ammonites pedernalis Binckhorst, 1873, Mon. Gast. et Céph. du Limbourg, p. 21, 
Pl. V a’, fig. 1 (no others). 
Sphenodiscus pleurisepta Bohm, 1898, Zeitschr. Deutsch. geol. Gesell, Vol. L, pl. 7. 
Conrad’s original specimens, preserved in the United States National 
Museum, show how erroneous and misleading are his descriptions and 
figures. The original of his figure has two distinct rows of lateral tubercles. 
Another specimen, 117 mm. in diameter, is the one cited as collected by 
Schott, “Yellow Stone.” This has the same characteristics, but is in the 
gerontic stage, and the outer row of tubercles disappears on the last 
quarter of the outer volution. The condition of the specimen, however, 
made this somewhat doubttul. 
A number of fine specimens were collected by Stanton and Vaughan 
near Kagle Pass, Tex. All of these have two rows of nodes on the sides, 
and one is a noble specimen 182 mm. in diameter (PI. IV, fig. 1-2). What 
appears to be the abraded edge of the aperture is present on one side, and 
the living chamber is somewhat over one-half of a volution in length. The 
inner row of nodes is present, but the outer row is replaced on the last 
volution in the gerontic stage by broad arcuate folds. These are visible 
throughout the volution on the side opposite to the one figured. ‘The 
venter broadens and becomes less acute on the third quarter of the outer 
volution and is rounded on the last quarter. It is obvious from this that 
the specimens described below were in some cases dwarfs, the range being 
considerable. 
The interesting fact in this large specimen is that the lobes and saddles 
vary but slightly from those of smaller fossils. The three principal saddles 
and the lobes are longer; there may be one or two saddles more, making 
the total number fourteen, concealed under the shell of the umbilical zone; 
and the marginals are more numerous, but otherwise the sutures are just 
about the same as at younger stages. There are only five divided saddles, 
the first to the fifth, as in younger stages, and the remainder are entire. 
Another fact is that the amount of involution decreases so slightly, even in 
