102 CARBONIFEROUS AMMONOIDS OF AMERICA. 



one-half the diameter. Umbilicus broad and shallow, one-tburth the 

 diameter, and a little over half the height of the last whorl. i 



Septa consisting' of an external lobe, two lateral, and a "suspensive" 

 lobe on the umbilical shoulders; the internal lobes are three in number, 

 long, narrow, and pointed; this gives eleven lobes in all for Paraleffoceras, 

 while Gastrioceras has only nine, -Ami Schistoceras has thirteen or more: 

 that is, four external lobes on each side, one on each umbilical shoulder, 

 and three internal. Schistoceras is the only Carboniferous member of the 

 Glyphioceratida? that is known to have more than three internal lobes. 



The type specimen is a septate cast that when complete must have been 

 at least 4 inches in diameter. The whorls are broader and rounder than 

 on P. iowensp. They are quite involute, and tlic unil)ilicus is narrow on the 

 young shell, becoming wider as the shell grows older. The surtace tif the 

 cast is smooth, no constrictions or other ornamentations appearing on the 

 older shell. On the younger shell the umbilical shoulder* show faint ribs, 

 that shade off into tine undulations on the sides. Hyatt lias shown the 

 same thing on P. iowense." But in the Texas specimen the ribs persist te) a 

 muoh later stasre than on that from Arkansas. 



Bimensions. — Although the specimen was not well preserved, the meas- 

 urements of the entu'e form could be taken. They were as follows: 



Millimeters. 



Diameter 7. - 5.5. 5 



Height of last whorl from iimbilicnis 2.7. .5 



Height of last whorl from t(jp of inner win irl 17.0 



Width of umbilicns 13. .5 



An inner coil taken out of the same specimen gave the following 

 measurements : 



Millimeters. 



Diameter 2S. .5 



Height of last whorl from umbilicus 12. 



Height of last whorl from top of inner whorl 7. .5 



Width of umbilii'us 6. 



These show the inner coils to be much lower, less highly arched, and 

 less embracing than the outer ones. 



Surface markw(/s. — On the inner whorls a trace of the shell is pre- 

 served, and is like that figured by Hyatt. The undulating stria^ are like 

 those common on the CTly]diioceratid?e. 



Sutures. — The sutures are like those of P. ioivense figured by ]\leek and 



"Second Ann. Rept. Geol. Surv. Texas, p. 3.55. 



