Geol.— Vol. I.] SMITH— COMPARATIVE STRATIGRAPHY. 379 



1897. Beyrichites, Diener, Himalayan Fossils, II, Part i. Cephalopoda of the 



Lower Trias, p. 74. 



1898. Beyrichites, Tornquist, Neuere Beitrage zur Geol. und Pal. Umge- 



bung von Recoaro, etc., p. 658. 



Type, Ammonites reuttensis Beyrich, 1867, Cephalopoden des Muschel- 

 kalkes der Alpen. Abhandl. k. Akad. Wiss. Berlin, 1866, p. 113, pi. i, fig. 4. 



Involute, laterally compressed, deeply embracing; umbilicus narrow, sides 

 slightly convex, venter narrowly rounded. Sides ornamented with weak ribs 

 which usually have a falciform bend. Septa of the ceratitic type, but with 

 the saddles slightly denticulated, in the transition to becoming ammonitic. 



Waagen established this genus to include ^^Meekoceras " 

 reuttense Beyrich, M. khanikofi Oppel, and M. mattirum 

 Mojsisovics, of the Muschelkalk of the Alps, but he placed 

 these in the family Ptychitidas. Diener has shown that 

 Beyrichites does not belong to the Ptychitidae, but he went 

 to the extreme of classing it as a subgenus under Meeko- 

 ceras. 



On account of the specialization shown by its sculpture 

 and the denticulated saddles the writer considers this as an 

 independent genus, in the family Meekoceratidge, as mark- 

 ing a distinct stage in the evolution of the group. As thus 

 defined this genus is confined to the Middle Trias of the 

 Alps, India, Asia Minor, and Nevada. 



E. von Mojsisovics^ has recently classed Beyrichites with 

 the Ceratitidge, and regards it as a probable offshoot from 

 Dinar ites. 



Beyrichites rotelliformis Meek. 



Plate XLV, Fig. 5; Plate XLIII, Figs. 13-14. 



1877. Gymnotoceras rotelliforme, Meek, U. S. Geol. Expl. Fortieth Paral- 

 lel, Vol. IV, p, III, pi. X, figs. 9-90. 



Involute, discoidal-lenticular, laterally compressed. Whorl high and in- 

 creasing rapidly in height, with flattened-convex sides and narrowly rounded 

 venter. Umbilicus narrow, umbilical shoulders abruptly rounded, with very 

 steep inner walls. The height of the whorl is slightly greater than one-half 

 of the total diameter, and the width is two-thirds of the height. It is 

 indented to about two-sevenths of its height by the inner whorl. The width 

 of the umbilicus is about one-sixth of the total diameter of the shell. 



Surface ornamented with numerous fine flexuous ribs and radial striae of 

 growth, with sigmoidal curve on the flanks, and a sharp forward bend just 

 below the abdominal shoulders. These ribs are strongest on the flanks, and 

 become obsolete near the venter. They do not become obsolete on the ma- 

 ture shell, although they are stronger on the young shell. 



1 Cephalopoden der Hallstatter Kalke, Bd. I, SuppleraentHeft, 1902, p. 331. 



