THE CRINOIDEA 



157 



LXX., and of tegmen in Fig. XXXIT. ; O rather small, pushed anteriorly, 

 and asymmetrical; tegminal lAmb and IIAmb distinctly visible ; arms fork 

 once or twice, stout, biserial, with large pinnules ; no cirri on column. The 

 large size of the cup is accompanied by development of stroma-strands across 

 the sutures. The large tegmen permitted a Gastropod (Platyceras) to attach 

 itself above the anus and live on the excrement ; this is seen in many of 

 the larger Adunata and Camerata and a few other crinoids (Keyes, 1888). 

 SUB-FAMILY 3. PLATYCRININAE. Platycrinidae with IBr 1 (rarely 2), IIBr 2 

 (rarely 3) ; tegminal Amb and iAmb usually more than in Coccocrininae, 



FIG. LXX. 



Marsipocrinus, from Brit. Mus. E6519. pn, pinnules ; other letters as usual. Nat. size. 



fewer than in Marsipocrininae ; anal tube often present ; section of stem 

 circular near the cup, elliptic or rhomboid below, with fulcral ridge following 

 long diameter ; lumen small and round. Genera Platycrinus, Miller 

 (1821, W. & Sp., 1897 ; synn. Centrocrinus and Pleurocrinus, Austin; 

 Edwardsocrinus, d'Orb.), Devonian (1 species), Carboniferous, Europe and 

 N. America (Fig. LXXI.) 1-3 iAmb always rest on the adjacent shoulders 

 of the RR in each IR, and consolidate a varying number of Br and Amb 

 with the calyx ; arms fork once to thrice (exceptionally more), the dichotomy 

 often irregular, producing 6 rami to the arm ; columnals have a slight 

 skew, so that the fulcral ridge of the proximal surface lies at an angle to 

 that of the distal surface ; thus the flattened stem, which otherwise could 



