SCIIISTOCERAS. 109 



saddles are long, narrow, and spatulate; the external lobe and the three 

 lateral lobes are long, narrow, pointed, and tongue-shaped. On the umbil- 

 ical shoulder is a fifth lobe, short and ])ointed, and on the dorsal side is a 

 long, narrow, and pointed antisijihonal lobe, flanked on each side by a pair 

 of lobes, of which the one nearest the dorsum is long and the second short, 

 like that on the umbilical shoulder. There are thus fifteen lobes and fifteen 

 saddles in all — one jiair more than those oi Acjafhireras and two pairs more 

 than those oi Paralef/ocerus. It is prosiphonate, but it could not he ascer- 

 tained at what stage tlie sijdional collars Ijegan io point forward. 

 The largest specimen seen had the following ilimensions: 



JlilUmeters. 



Diameter 69 



Height of last whorl 35 



Height of last whorl fr( mi the preceding 23 



Width of last whorl 3,5 



Width of umbilicus 14 



Involution 12 



This specimen Avas septate throughout, and the outer shell showed the 

 impressions of the septa of nearly one-half a revolution in addition to this. 

 The body chamber would have added at least three-quarters of a revolution 

 more, so that the full diameter of this shell could not have been less than 

 17.") mill. 



The type of this species served Professor Hyatt as the type of his 

 genus Schistoceras, and to his kindness the writer owes the use of the 

 specimens. Since a specific name was never given to this form, the 

 designation Schistoceras hyatii is appropriate. 



This species is nearest to S. hUdrethi Morton, Ijut differs from it in 

 being more compressed laterally, in the greater height of the whorl, in the 

 slightly narrower nmbilicus, and in the fainter umbilical ribs, which persist 

 to a later stage in 8. hildrethi. 



Occurrence. — This species is at present known only from the Upper 

 Coal Measures, Cisco formation, of Graliam, Tex. Specimens of it, includ- 

 ing the t3'pe (PL XX, figs. 5 and 6), are in the private collection of the late 

 Prof Al])heus Hyatt, of Cambridge, Mass.; in the Museum of Comparative 

 Zoology; and in the U. S. National Museum. 



Ontogeny. — Since the individual development of this species shows its 

 2:)hylogeny in the plainest terms, it is given below, so far as could be 

 ascertained. 



fe 



