CEPHALOPODA— AMMONOIDEA, 143 



215. G. calyx Phillips. (Fig. 1394, a-r.) Mississippic. 

 Small (6 mm. or less), with wide, open umbilicus, and about 



three faint constrictions to a whorl ; surface ornamented with fine, 

 smooth cross striae ; suture with incipient ventral saddle. 



St. Louis-Chester (Fayetteville shale) of Arkansas; Vise of 

 western Europe. 



LXXXVI. Gastrioceras Hyatt. 



Evolute goniatites, with open umbilicus, trapezoidal or semi- 

 lunar cross section, and usually ribs or tubercles on the sides; 

 suture with nine lobes, only a single pair visible on the sides. 

 Devonic-Carbonic. 



216. G. branneri Smith. ( Fig. 1 394, J-/. ) Mississippic. 

 Discoidal ; comparatively narrow ; umbilicus very large ; whorls 



mcreasing very slightly; ribs strong on umbiHcal margin. 

 Chester of Arkansas. 



217. G. carbonarium von Buch. (Fig. 1394, ^, /j.) Carbonic. 

 More involute than preceding, with smaller umbilicus, sharply 



angulated umbilical shoulder, and stronger ribs extending half way 

 to venter. 



Middle Coal Measures of England, Belgium and Germany, and a 

 similar horizon in Coal Measures of Arkansas. 



218. G. entogonum Gabb. (Fig. 1395, a, Z?.) Mississippic. 

 Smaller and broader than the preceding with conspicuous longi- 

 tudinal striae. 



Chester of Texas, etc. 



219. G. globulosum M. and W. (Fig. 1395, c-^.) Carbonic. 

 Very globose ; whorls much wider than high ; umbilicus about 



one third diameter of shell; angle of umbilicus 45° ; lobes narrowly 

 pointed; surface smooth. 



Cisco of Texas; Upper Coal Measures of Illinois; Middle Coal 

 Measures of Arkansas. 



220. G. listeri Martin. (Fig. 1395, /-/i.) Carbonic. 

 Of moderate width, with sharp, short umbilical ribs, and large 



umbilicus. Differs from G. carbonarium chiefly in its greater pro- 

 portional width of whorls, the stronger umbilical ribs and broader 

 lateral lobes. 



