GENUS BRANCOCERAS. 217 



tliickciuMl rim wliicli is prodiiccMl on vac\\ side into a loiiti', fiat, spinc-litcc process 

 projecting neai'ly at riglit angles to tlic longitndinal axis of tlie shell. 

 Carboniferous. 



74. Acauthonautilus liispiuosiis. 



GpnuR AsvMPTOcERAS {Et/chhnlf, 1852, emend. TTi/aff, 189:1). — Shell Naviiliai-Wke, 

 with subquadrate whorls. Body-chaml)er contracted in some species ; the aperture 

 may have the inferior border thickened into a prominent lip, or there ma}' l)e a 

 distinct inflation just below this border. Siphuncle at the margin of the periphery 

 just beneath the test. 



Carboniferous. 



75. Asymptoceras erassilabrnm.* 76. Asymptoceras Foorcli. 



Genus Solenocheiu'S {Meek tnul Wmihen, 1870, emend. Ihjaft, 1883, 1893).— 

 Shell NiiiitihisAWo, subglobose. Cross-section broadly sagittate. Periphery 

 elevated and rather narrowly rounded, the umbilical angles of the aperture \)vo- 

 jecting on each side. Siphuncle marginal as in Asym.'ptoceras. 



Carboniferous. 



77. Soleuoebeilus dorsalis. 78. Solenochoihis ? Hibeniicus. 



70. Soleuofheilus clausus.* 



SuB-GRnEii AMMONOIDEA. 



FimUy — Geyphiocer.vtid.e, IIiiatt,\iiS?i (emend. J. Perrin Smith, 1897; Hyatt, 1900). 



[Siib-onlcr Eiiri/campyli, Hyatt, 1000 (pai-s), in Eastman's transl. of von Zittpl"s ' Grunilz. d. 

 Paloeout.'] 



Shells of variable form, including highly involute ones and also some with open 

 umbilicus exposing all the inner whorls. Septa concave along the median line of 

 the periphery in Brancoccras, the primitive form, convex in the mature stages of 

 other genera ; peripheral lobe entire in primitive forms, but becoming divided in 

 more specialised genera ; lateral saddle simple or, very rarely, divided ])y a second 

 lateral lobe. Siphuncle small ; septal necks short, usually with a forwardly- 

 directed collar. 



Genus Bu.vxcoeioii.vs {Hijatt, If'iSZ). — Shell involute, discoidal and compressed; 

 uml)nicus narrow or closed ; surface of test smooth or with line transverse ribbing; 



