﻿491 



Trocholites scoticus. 



Nautilus (Troch.) scoticus, Blake {Brit. Ceph., PL xxix, Fig. 6, 

 PI. xxviii, 1-4). 

 Blake's figures show sutures, but he states that none are discern- 

 ible. The aperture and form of whorl and striae indicate that this 

 is a species of Trocholites. 



HercoceratidcE . 



In "Carboniferous Cephalopods," second paper, Fourth Annual 

 Report Geol. Survey of Texas, I separated the Tainoceratidae, includ- 

 ing the Temnocheilus, Metacoceras and Tainoceras from the Her- 

 coceratidas, but further study leads me to think that this is not 

 advisable considering the approximation in form and characters of 

 the two sets of genera and have reunited them here under the old 

 name. 



In genera of fossil Cephalopods I regarded Ptyssoceras {Cyrt.) 

 alienum, sp. Barrande, as the arcuate radical type of this family. 

 It has a single row of large, lateral tubercles, sutures nearly straight, 

 whorl in section depressed, elliptical and siphuncle ventral, and it 

 has no dorsal furrow. The genera properly included under this 

 family name are as follows : 



Ptyssoceras, Trochoceras, Hercoceras, Anomaloceras, Lower 

 Silurian ; Centroceras, Devonian ; Temnocheilus, Devonian to 

 Dyas (Permian) ; Metacoceras, Tainoceras, Carboniferous and 

 Dyas ; Foordiceras,* Dyas. 



I have also provisionally placed Coelogasteroceras in this family 

 on account of the general resemblances of the form of the nepionic 

 stage, the smooth shell and the hollow ventral zone in the abdomen. 



Ptenoceras,-\ n. g. 

 Under this name I propose to place all those forms formerly in- 

 cluded under the name of Hercoceras in my Genera of Fossil 

 Cephalopods, whether turbinate or coiang in the same plane, which 

 have no impressed zone at any stage. The whorls are open, or 

 barely in contact, and are rounded in the early stages andsubquad- 

 ragonal later in life. The apertures are similar to those of Herco- 



*A11 these genera are mentioned or redescribed below as far as needed for the pur- 

 poses of this paper except Foordiceras and Tainoceras, which have been described m 

 "(Jaiboniferous Cephalopods," quoted above. 



i]l7r],u$, winged. 



