310 COMPARATIVE ANATOMY CHAP. 



indistinctly arranged in two to three rows. The anal interradial carries a short 



ir 



CO 



FIG. 255. Taxocrinus multibrachiatus, Ly. 

 and Cass. ir, ir^, and ir. 2 , Interraclials ; di, dis- 

 tichals ; ba, basals ; ib, infrabasals ; co, stem ; r, 

 radials ; c\, Co, and 03, primary brachials. 



FIG. 256. Thaumatocrinus renovatus. 

 P. H. C. (after P. H. Carpenter). Calyx 

 from the anal side, cj, c-2, and 03, Primary 

 brachials ; r, radials ; c, points of insertion 

 of the cirri ; cd, centrodorsal ; ir, inter - 

 radials ; ia, interradialia analia ; pa, proces- 

 ses analis ; ta, tubus analis ; p, pimmlee. 



jointed appendage, 

 arms with pinnulre. 



Besides this there is a short anal tube. Five unbranched 



Order 4. Canaliculata. 



Calyx symmetrically five-rayed. Base dicyclic, the infrabasals usually not 

 separate, but atrophied or fused with the proximal columnal 5 basals, occasionally 

 not externally visible. Each radial is followed by 2 costals. Anal plates always 

 wanting (hence the regularity of the calyx). Interradials with few exceptions 

 wanting. Arms simple or divided (one to ten times). Tegmen calycis usually flat, 

 with open mouth and ambulacra appearing at the surface. Orals rarely present. 

 Tegmen calycis often plated with small loose-lying plates. Stem present either only 

 in young forms or also in adults. Basals and radials perforated by dorsal canals. 

 To this order belong, besides Mesozoic and Tertiary forms, most of the extant 

 Crinoids. 



Family 1. Apiocrinidae. 



Calyx consists of 5 basals of equal size, 5 radials and 2x5 primary brachials. 

 Distichals may also take part in its formation. Interbrachials and interdistichals 

 may occur. Tegmen flexible, with small plates. Arms more or less branched, con- 

 sisting of a single row of joints. Stem without cirri, usually expanding in its 

 proximal region to the same width as the calyx, but not containing the viscera. 

 Jurassic, to present. Apiocrinus, Millericrinus, and the extant Calamocrinus. 



Family 2. Bourgueticrinidse. 



Calyx consists of 5 basals and 5 radials. Brachials connected in pairs by 

 syzygial sutures. Five orals in the tegmen calycis. Interambulacral region other- 

 wise not plated. Ambulacra with covering plates, but without lateral plates. Stem, 



