MOLLUSC A—CEPHALOPODA. 33 



j. Shell strongly compressed 888. 



888. Venter channeled 11. 



11. Superior saddles strongly notched (ammonitic), the others 



simple XCV. Medlicottia. 



11. Superior lateral saddles not notched I2t- 



I2t. Umbilicus small XCIX. Sageceras. 



I2f. Umbilicus closed C. Pseudosageceras. 



888. Venter not channeled mm. 



mm. Superior lateral lobe only divided ; others pointed, venter 



broadly rounded.. XCI V. Pronoritesi 



mm. Most of the lobes serrately divided, venter narrowly rounded. 



XCII. Prodromites. 

 •. Lobes mostly dissimilar and not numerous ; serrations more than two or 



three in each lobe k. 



k. Shell laterally compressed 999. 



999. Venter sharply acute, often keeled nn. 



nn. Umbilicus small or closed, surface smooth I3f. 



I3f. With adventitious ventral lobes, second lateral largest. 



XCVIII. Aspenites. 

 I3|. Without adventitious lobes, third lateral largest. ■ 



CIV. Longobardites. 

 nn. Umbilicus moderate, surface ribbed and noded. 



cm. Eutovioceras. 



999. Venter rounded or obtusely angular 00. 



00. Umbilicus small, surface smooth or nearly so. 



XCVII. Paranannites. 



00. Umbilicus moderately large I4f. 



I4f. Surface smooth CII, Meekoceras {Prionolobus). 



I4f. Surfate with low ribs /. 



/. Saddles faintly crenulated. 



CII. Meekoceras {Beyrichiies). 



I. Saddles smooth CII. Meekoceras [Koninckites). 



I4t. Surface strongly ribbed m. 



in. Nodes faint or absent, ribs numerous 7''. 



7^. Venter keeled, saddles and lobes finely serrate. 



C V 1 1 . Ceratites ( Gym n otoceras ) . 



7''. Venter not keeled ; lobes deeply and complexly 



notched ; saddles entire. ..^.CVIIl. Acrochordiceras. 



ni. More or less strongly noded or with spines ; ribs 



coarse 8^. 



%' . Nodes or spines on ventrolateral margin only. 



CVI. Tirolites. 

 V . A second row of nodes near umbilicus. 



CVII. Ceratites. 



999. Venter flat pp. 



pp. Umbilicus moderate with abrupt shoulder... CII. Meekoceras. 

 pp. Umbilicus large, shoulder abrupt, sides flat. 



CII. Meekoceras ( Gyron ites ) . 

 k. Shell discoidal, whorls rounded or subquadrate, umbilicus large. 



0000. 



