GENUS BRANCOCERAS. 217 



thickened rim which is produced on each side into a long, fiat, spine-like process 

 projecting- nearly at right angles to the longitudinal axis of the shell. 

 Carboniferous. 



74. Acantlionautilus bispinosus. 



Genus Asymptoceeas (Rychholt, 1852, emend. Hyatt, 1893). — Shell Nautilus-like, 

 with subquadrate whorls. Body-chamber contracted in some species; the aperture 

 may have the inferior border thickened into a prominent lip, or there may be a 

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

 just beneath the test. 



Carboniferous. 



75. Asymptoceras crassilabrum.* 76. Asymptoceras Foordi. 



Genus Solenocheilus (Meek and Worthen, 1870, emend. Hyatt, 1883, 1893).— 

 Shell Nautilus-like, subglobose. Cross-section broadly sagittate. Periphery 

 elevated and rather narrowly rounded, the umbilical angles of the aperture pro- 

 jecting on each side. Siphuncle marginal as in Asymptoceras. 



Carboniferous. 



77. Solenocheilus dorsalis. 78. Solenocheilus ? Hiberuicus. 



79. Solenocheilus clausus. 



Sub-oedee AMMON01DEA. 



Family — G-ltphioceeatid^:, ni/att,188d (emend. J. Perrin Smith, 1897; Hyatt, 1900). 



[Sub-order Ewrycampyli, Hyatt, 1000 (pars), in Eastman's transl. of von Zittel's ' Grumlz. d. 

 Palaeont.'] 



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

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

 the periphery in Brancoceras, 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 by a second 

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

 directed collar. 



Genus Beancoceeas {Hyatt, 1883). — Shell involute, discoidal and compressed; 



umbilicus narrow or closed ; surface of test smooth or with line transverse ribbing; 



