GENUS GASTRIOCERAS. 219 



Sub-genus Beykichoceeas, sub-gen. nov. (= GlypMoceras, Section II [pars], of 

 Hyatt). — Shell involute, usually compressed, with rounded, sometimes depressed 

 periphery, umbilicus variable, generally small. Surface of test usually smooth or 

 only marked with lines of growth, rarely with transverse ribbing or with spiral 

 strise. Suture-line resembling that of Sphenoceras, but with the peripheral saddles 

 rounded or linguiform, never acutely pointed; peripheral lobe usually shallow, 

 median saddle small and larval in shape ; lateral lobes acutely to obtusely pointed, 

 sometimes mucronate ; lateral saddles broadly rounded, when less so the apex 

 points towards the peripheral saddle on each side. 



97. Beyrichoceras obtusum. 10G. Beyrichoceras micronotum. 



98. „ truncatum. 107. ., diadema. 



99. „ sub truncatum.* 108. „ reticulatum. 



100. „ occidentale.* 109. „ subreticulatum.* 



101. „ difficile.* 110. „ bilingue. 



102. „ subquadratum.* 111. „ Davisi. 



103. „ sphseroidale. 112. „ eordaturn. 



104. „ Browni. 113. „ pulchellum.* 



105. „ corpulentum. 114. ,, spirale. 



Sub-genus Muensteroceras (Hyatt, 1883). — Shell globose to subglobose and 

 compressed ; umbilicus of variable dimensions ; whorls higher than wide ; surface 

 of test with more or less regular lines of growth, or with reticulate lines. Suture- 

 line— peripheral lobe deep, often with subparallel sides; the median saddle small as 

 in Beyrichoceras ; peripheral saddles rounded or spatulate ; lateral lobes acutely to 

 obtusely pointed ; lateral saddles broadly rounded, or forming a wide-spreading 

 shallow arch. 



115. Mueusteroceras crassum.* 116. Muensteroceras ellipsoidale. 



117. Mueusteroceras obesum.* 



Genus GtASTEIOOEEAS (Hyatt, 1883, emend. Karpinsky, 1889). — Shell globose or 

 subcompressed, with trapezoidal cross-section, usually widely umbilicated, whorls 

 numerous, periphery broadly rounded. Surface of test with longitudinal striae, or 

 with transverse ribs, the umbilical margin usually bearing tubercles or tubercular 

 ribs ; constrictions often present ; suture-line — peripheral lobe broad and sometimes 

 with mucronate terminations {G. Jossx, e. g.), divided by a broad and elevated 

 median saddle ; peripheral saddles broadly rounded, or spatulate ; first lateral lobes 

 deep, linguiform, with mucronate extremities in some species; second lateral lobes 

 small, angular, situated upon the umbilical margin, or upon the inner (umbilical) 

 area; lateral saddles sometimes broadly, sometimes narrowly rounded or spatulate. 



Carboniferous and Permo-Carboniferous. 



118. Gastrioceras circuinuodosuni.* 119. Gastrioceras circuniplicalili' 



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