194 



THE CRINOIDEA 



forming a closed ring and 5 RR 

 with high muscle-plates ; arms in- 

 corporated to a very slight extent 

 in the cup ; and then only loosely 

 without development of iBr ; all 

 columnals, or all except those in 

 the proximal region, have ellipti- 

 cal joint-surfaces with a grooved 

 and toothed fulcral ridge in the 

 long diameter and ligament-fossae 

 on either side of it ; each colum- 

 nal is twisted so that the ridge at one end 

 lies at an angle to that at the other end ; cirri 

 may be present at the root end or in the 

 middle of the stem. Sacculi occur in recent 

 forms. Genera Bourgueticrinus, d'Orbigny 

 (1840), Cretaceous, Europe and Alabama (Fig. 

 CXV.) ; sides of cup vertical or sloping in- 

 wards above ; BB about half height of RR ; 

 radial facet small, horizontal, with small 

 dorsal ligament - fossa ; IBrj -y^ 2 laterally 

 connected with adjoining rays, arms un- 

 known ; proximale enlarged, circular ; colum- 

 nals of proximal region circular, widening 

 upwards ; those of middle and distal regions 

 twisted, elliptical ; fulcral ridge continuous 

 around axial canal, ligament-fossa broad and 

 shallow ; cirri rare except at root Meso- 

 crinus, P. H. Carpenter (1881), Cretaceous, 

 Sweden, Germany ; sides of cup slope out- 

 wards ; BB short ; radial facet large, slopes 

 upwards to centre, with larger ligament-fossa ; 

 arms unknown; proximale small and circular; 

 proximal columnals circular, narrowing up- 

 wards ; the rest as in Bourgueticrinus, but liga- 

 ment-fossa deeper ; cirri sometimes numerous. 

 Rhizocrinus, M. Sars (186 4, -68; synn. Cono- 

 crinus, d'Orb. ; Democrinus, Perr.), Eocene 

 to Recent ; Atlantic, 73 to (?) 1900 fathoms ; 

 sides of cup slope slightly outwards ; BB 

 high, may be 7 times height of RR, often 

 fused ; radial facet slopes upwards to centre, 

 with small ligament - fossa ; IBrj and 2 free 

 laterally, arms not forking ; proximale thin 

 and discoidal ; proximal columnals discoidal, 

 those of middle region slender, fulcral ridge 

 broken at axial canal, around which the 

 ligamenkfossa is concentrated (Fig. XLIX. 

 7) ; no cirri except at root (Fig. CXVI. ; see 



Rhizocrinus lofoten- 

 sis, North Sea, about 

 twice nat. size. (From 

 Narrative of the Cruise 



f H.M.S. "t'lwllen- 

 r.") 



