90 CARBONIFEROUS AMMONOIDS OF AMERICA. 



The septa are exactly like those figured by Meek and Worthen, so 

 that no further description of them is necessary; tliey are typical of the 

 genus Gastrioceras, as characterized by Hyatt, although as Karpinsky" 

 remarks, the sutures alone are not sufticient to separate the genera 

 Glyphioceras and (iastrioceras, since a comparison of the sutures of 

 Gastrioceras jossca Verneuil and Glyphioceras diadema Verneuil (not Goldfuss) 

 shows the almost perfect similarity of the two. 



The surface of the shell was unknown to Meek and Worthen, but some 

 of the Arkansas specimens have the shell partially preserved. It is marked 

 with fine, sharp, doubly arcuate, sickle-shaped striae or ribs, with the sinus 

 on the ventral portion pointing backward. The surface ornamentation 

 resembles that of Glyphioceras ohtusum Phillips,'' but the form is nuich more 

 globose, and the lobes unlike those of Phillips's species. 



Dimeiisioiis. — (^ne of the fragments shows a diameter of over 2 inches; 

 on this only the body whorl was seen, it being at least one coil in length. 



Diiiifiisiimt: of the larfji'nt fiijured uperlmi'ii. 



Millimeters. 



Diameter '^t' 



Breadth 27 



Height of last whorl 14 



Height of last whorl from center of mnliilicus 19 



Height of last whorl from top of the inner one 8 



Width of viinl)ilii-us 9 



These measurements show the adult shell to be very globose. 



Occurrence. — Several specimens of this species were found in the Mid- 

 dle Coal Measures of Scott County, Ark., T. 1 N., R. 28 W., sec. 4, SE. 

 4 of SE. 4. This species is also found in the Cisco formation of the 

 Texas Upper Coal Measures, and in the Upper Coal Measures of Spring- 

 field, 111. The specimen figured on PI. XXI, figs. 7-9, cauie from the 

 Upper Coal Measures, Cisco formation, of Graham, Tex., and has been 

 deposited by the writer in the U. S. National Museum. 



"Animoneen der Artinsk-Stufe, p. 46. 



6Geol. Yorkshire, Pt. II, \>. 23.5, PI. XIX, figs. 10-13. 



