134 University of Texas Bulletin 



found loose on Pennyslvanian strata near the boundary of the Permo- 

 Carboniferous and may also belong to this latter horizon. All of them 

 show only five to six lobes, while another species in the higher part of 

 our Permo-Carboniferous (Word formation) shows about seven lobes; 

 and anotker one, of an entirely different form and externally similar 

 to the Sicilian Popauoceras, shows about ten lobes. 



If we compare not only the external lobes of the group represented 

 here but also the internal ones which could be very well observed in 

 M. Smithi, we find that they are absolutely different from those of the 

 Sicilian type, which are known in St. mediterraneum^ and in St. 

 Benedictinum.^ While we see that the trifid antisiphonal lobe in the 

 Sicilian species is not much, if at all, deeper than the following lateral 

 lobes, we observe in M. Smithi (pi. VI, fig. 79, 80) a very deep lance- 

 olate antisiphonal lobe that ends in a quite sharp point. At both sides 

 of it, we see a low and slender rounded saddle, after which follows a 

 much broader and much higher saddle, separated from the smaller one 

 by a narrow, pointed, asymmetrical lobe which is much less deep than 

 the central antisiphon'al lobe. We may probably consider these three 

 central lobes with their two small dividing saddles as a very broad 

 and deep, trifid, antisiphonal lobe. The same arrangement of the in- 

 ternal lobes has been observed in Marathonites vidriensis n. sp. (pi. 

 VII, fig. 31, 32). This antisiphonal lobe resembles the totality of the 

 internal lobes of Gastrioceras. We shall also see that there is another 

 new subgenus of Stacheoceras from the same locality and the same 

 horizon which shows a similar form of the antisiphonal lobe, although 

 the rest of the internal lobes are somewhat different. 



J. P. Smith^ has drawn the internal suture of Stacheoceras Ganti 

 but he has not been able to distinguish the details. At least, nothing 

 is shown there of the characteristic antisiphonal lobe of Marathonites. 

 Our species have a great external resemblance to those mentioned 

 above from the Russian Artinsk and those from the Pennsylvanian of 

 America, not only in the form of the shell but also in the limited num- 

 ber of lobes between the sipho and the umbilical shoulder; but owing 

 to our imperfect knowledge of the inner lobes of the species mentioned, 



'Gemmellaro, Ipc. cit., app., pi. C, fig. 8. 



"Gemmellaro, loc. cit., app., pi. C, fig. 6. • 



»J. P. Smith, loc. cit., p. 13,2, pi. 21, fig. 16. 



