still needs revision, since no doubt sonic of the geologically 

 younger Arietites have been improperly included here. Another 

 point, which needs thriller investigation, is the relation of many 

 forms to the group of ^K<j. (i/x/l(i/>/ in. Schloth. 

 Ninety-six species. 



HARPOCERAS ACTION, d'Orb. T. 108, figs. 627. lii'x. 

 BIFRENS, Brug. T. 103, fig. 556. 



SF.KI'KNTIM M. Schl. T. 103. tigs. ;V>X. 559. 

 Genus OPPELIA, Waagen. 



Shell with umbilicus usually narrow, external side either 

 rounded only on the 1 tody-chamber or on all the whorls. Sculp- 

 ture sickle-shaped, body-chamber frequently geniculate, never 

 cariuate or angular, embracing one-half to two-thirds of a whorl ; 

 margin of aperture sickle-shaped or with cars, always with 

 rounded external lobes. Siphon stout with calcareous sheath. 

 Aptychus divided, calcareous, thick, folded (Apt. lamellosus) ; 

 muscles of attachment near the margin in the lower half of tin- 

 shell. Lobes moderately branched, siphonal mostly shorter 

 than the first lateral; lobular bodies slender with almost parallel 

 edges; lateral lobes divided into two principal symmetrical 

 branches. 



Oppelia branches off in the lower Oolite with Opp. subradiata 

 from Harpoceras; the last representatives, as far as we know, 

 appear in the upper Jura of Stramberg, where a considerable 

 number of different forms are found. 



Seventy-one specie^. 



OPPELIA SUBRADIATA, Sowb. T. 110, fig. 650. 



Genus HAPLOCERAS, Zittel. 



The genus Haploceras was established by Zittel for a group 

 allied to Oppelia from the middle and upper .Jurassic, which is 

 characterized by vrry feeble or no sculpture; also some creta- 

 ceous forms, as I/d/il. Grm<tiini m are placed here; and with 

 them forms very pronounced wrdgr- <>r chisel-shaped in section, 

 afl //'!/>!. /H-///.S : finally, spi-cio with quite sharp external sides, 

 as f/a/if. /'/s//.s. Orb. 



In otlie' .lurassie species of //tijilorrrfit*. there is gradually 

 . |. -v. -loped a transverse sculpture, which is contim-d to tin 



