CLASS III CRINOIDEA 197 



This feniily represents another line of profuse crinoidal development characteristic of the 

 Mississippian area in the United States, parallel to that of the later Batocrinidae. It may be 

 considered as a direct branch from that family, but sharply and consistently distinguished 

 from it by the fact that the anal plate is followed by two plates instead of three. It was 

 short lived, being restricted to the lower part of the Lower Carboniferous, where it culminated 

 in large and striking forms, not found outside of the Mississippi Valley. Only two of its genera 

 are certainly known to occur in the approximately equivalent formation of Europe. 



§ 1 . Tegmen composed of well differentiated plates, with anus at the end of a tube, 

 a. Interbrachials connecting with the tegmen. 



Amphoracrinus Austin. Calyx lobed, the largest part above the arm zone ; 

 rays widely separated. Interbrachials few. First primibrachs usually quad- 

 rangular, sometimes hexagonal. Arms stout, either simple or branching, 

 biserial below and above the bifurcations. Anal tube short, eccentric. Oral 

 plates often strongly spiniferous. Anal plate exceptionally followed by three 

 plates in the second range. Lower Carboniferous ; AYaverly to Lower Bur- 

 lington Group in the United States, and lower part of the Mountain Lime- 

 stone in Britain. 



This genus is a transition form from the Batocrinidae, in which the Actinocrinoid structure 

 of the anal side has not become constant. In some species the middle plate of the second row 

 has not been entirely eliminated, but occasionally appears in diminished size, and scarcely 

 touching the anal plate. This is consistent with its geological position as one of the earliest 

 of its family, and one of the first to disappear. 



Actinocrinus Miller {Amphora Cumb. ; Phillipsocrimis M'Coy; Blairocrinus 

 S. A. Miller) (Fig. 299, D). Calyx lobed, rays widely separated ; largest part 

 below arm zone. Interbrachials numerous. First primibrachs usually 

 hexagonal. Rays within the calyx bifurcating alternately from every second 

 or third plate above the first. Arms either simple from the calyx, or 

 branching, and biserial below as well as above the bifurcations. Anal tube 

 long, central. Lower Carboniferous; Lower Burlington to Keokuk, in the 

 United States, and Mountain Limestone of Britain and Belgium. 



Stegamcrinus M. and W. {Samp)so)iocriiius M. and G.). Calyx similar to that 

 of Actinocrinus, but relatively lower, and having the rays produced into one 

 (♦S*. sculptus) or two (S. pentagonus) tubular extensions giving off pinnulate arms 

 alternately at the sides. Anal tube small. Lower Carboniferous (Lower and 

 Upper Burlington) ; North America. 



p. Interhrachials not connecting with tegmen. 



Cactocrinus W. and Sp. (Fig. 299, A, B). Calyx not lobed. Arms usually 

 strong, twenty to forty, unbranched, about equidistant, given off in a more or 

 less continuous ring, and directed upward ; bifurcations beyond the costals 

 from every successive brachial. Anal tube long, central. Lower Carboni- 

 ferous (Kinderhook to Lower Burlington) ; North America, (? ) Belgium. 



Teliocrinus W. and Sp. Similar to the last, but arms more slender and 

 numerous, usually sixty or more, their lower portions directed outward, and 

 forming a broad continuous rim. Lower Carboniferous (Upper Burlington) ; 

 North America. 



§ 2. Tegmen of undifferentiated plates. Anus directly through the tegmen, without 

 a tube. 



Physetocrinus W. and Sp. (Fig. 299, C). Interbrachials connecting with 

 tegmen. Calyx rotund, lobed, with arms in groups, stout ; tegmen rounded 



