

102 PALAEONTOLOGY OF ILLINOIS. 



In the perforated clmracter of the umbilicus, the shells of this group may 

 not differ from some other sections of discoid fossil Nautili, but in the posses- 

 sion of several distinct revolving grooves and angles, with strong longitudinal 

 striae, they seem to be quite peculiar. The group appears to be mainly, if not 

 almost exclusively confined to the Carboniferous system, and will include the 

 following foreign species : Nautilus sti/gialis, N. Edwardsianus, N. Omalianus 

 and N pingtns* de Koninck, together with N. sulcatus, N. cariniferus, etc., 

 of Sowerby. 



After proposing the foregoing name and description for this aneient group of 

 Nautili, we observed that Prof. McCoy had proposed in his "Carboniferous 

 Fossils of Ireland," p. 20, 1844, the name Temnochielus, for a group of Carbon- 

 iferous species, including some of the same species for which our name Trema- 

 todiscus was proposed. As his subgenus, however, embraced a much wider 

 diversity of forms than ours, it may be found convenient to restrict it to such 

 types as his first species N biangulatus, N. pinguis (McCoy, not deKon.), 

 and N globatus, as proposed by one of the writers (Palseont. Up. Mo., p. 64), 

 during the past year ; while Trematodiscus may be retained for the forms agree- 

 ing with the types for which it was proposed. 



As noticed in the Palaent. Up. Mo., above cited, Blainville had in 1824 

 (Dect. Sc. Nat. Tom. XXXII, p. 185), included some of the same forms fall- 

 ing within the group Trematodiscus, in Montfort's proposed genus Simplegades, 

 but it is evident from Montfort's figure and description, that his type of Sim- 

 plegades, was an Ammo7iite or a Ceratite, and hence his name could not prop- 

 erly be retained for the forms under consideration. 



(x. B. Sowerby (Conch. Man., 276, 1842) also falls into the same error, and 

 places Nautilus sidcatus, Sowerby, under Montfort's name Simplegas, or Sim- 

 plegades, and yet admits that Montfort's type has sinuous septa like the Ammo- 

 nites. 



Nautilus (Trematodiscus) trisulcatus, M. and W. 



PI. 14, Fig. 10 a, 10 6, 10 c. 



Nautilus (Discus) trisulcalus, Meek and Worthen, Oct., 1860. Proc. Acad. Nat. Sci., 



Philad., p. 470. 

 Nautilus (Trematodiscus) trisulcatus, M. and W., June, 1861. lb., p. 148. 



Shell under medium size, discoidal; umbilicus wide, of 

 moderate depth, and showing nearly all of each inner whorl, 



* Not N. pinguis, McCoy. 



