130 University of Texas Bulletin 



Dimensions: 



I II III IV 



Diameter: 19.1 mm (1) 20.6 mm (1) 23.7 mm (1) 33.3 mm (1) 



Width 6.8 0.36 7.4 0.36 ?8.0 0,34 ?7.7 0.23 



Height of last whorl 10.2 0.53 10.6 0.51 12.5 0.53 17.3 0.52 



Diameter of umbilicus. . . 2.2 0.12 2.4 0.12 ?3.2 0.14 4.0 0.12 



These dimensions are measured on relatively small specimens ; there 

 are fragments the diameter of which must reach at least 36 mm. 



Relation to other species: 



If only the outer form and the ornamentation had to be considered, 

 this species would have to be regarded as a typical Popanoceras similar 

 to the younger individuals of P. Moelleri Gemm.^ or P. clausum 

 Gemm.^ But the suture does not leave any doubt that the species be- 

 longs to Stacheoceras. It is true that the suture could be seen only on 

 specimens which do not show even a trace of ornamentation, but on one 

 of the individuals with preserved shell a few of the entire and rounded 

 saddles show up rather clearly, and the relations of dimensions are so 

 similar (compare especially No. i, with suture line but without orna- 

 mentation; and No. 11, with ornamentation but not showing the septa) 

 that I do not doubt that all the specimens belong to the same species. 



Among the fauna of the Russian Artinsk we find a form which in 

 its outline and in the form of the ribs somewhat resembles our species. 

 It is Stacheoceras Lahuseni Karpinsky,^ but the prominent ribs which 

 are so very characteristic are missing in our specimens. 



Among the Sicilian species there is Stacheoceras Karpinskyi Gem- 

 mellaro* which, although much more subglobose than our species, 

 shows a strong curving backward of its ribs on the ventral part. 



Our species consequently is not entirely an exception but it does 

 not resemble very much any of the species described until now. A 

 somewhat extraordinary feature might be found in the circumstance 

 that the first lateral lobe of our species ends in four points ; the suture 

 on a small specimen shows that this lobe there is simply bifid. We notice 

 a similar development in the first lobe of Stacheoceras Krasnopolskyi 

 Karp.,^ but the character of the suture of this species is entirely dif- 



"Gemmellaro, Calc. c. Fusulina, p. 21, pi. 3, fig. 6-16. 

 =Gemmellaro, ibid., p. 22, pi. 3, fig. 17-21.' 



"Karpinslty, Amm. d. Artinsk-Stufe, p. 67, -pi. 5, fig. 1 a-h, 2 a-c, 3. 

 'Gemmellaro, Calc. c. Fusulina, p. 30, pi. 8, fig. 6-8. 

 "Karpinsky, Amm. d. Artinsk-Stufe, p. 73, pi. 5, fig. 10. 



