30 



CANADIAN FOSSILS. 



Genus Carabocrinus, Billings. 



(Carabocrinus, Report Geological Survey of Canada, 1856, page 275.) 

 Formula : 



Basal plates, 5. 

 Sub-radial plates, 5. 

 Radial plates, 1X5. 



Regular inter-radials, 0. 

 Azygos inter-radials, 3. 



Fig. 12. 

 Figure 12. Diagram of the structure of the cup in the genus Carabocrinus. 



Generic characters. — Cup, globular or ovoid ; basal plates, five, four 

 of them pentagonal, and the fifth hexagonal; sub-radials, five, three 

 of them hexagonal, one heptagon al, and one pentagonal, the latter 

 smaller than the others ; primary radials, five, each bearing an arm 

 which is several tunes divided. The azygos inter-radius is rather 

 large, and occupied by three plates. One of them is supported upon 

 the hexagonal basal plate ; a second upon the small pentagonal 

 sub-radial ; the third is situated between the two anterior primary 

 radials, its upper edge forming the margin of the cup, and its two 

 lower sides resting upon two of the upper sloping sides of the first 

 and second azygos plates. 



Upon the ventral surface five calycinal ambulacral grooves radiate 

 from the centre (where there appears to be an aperture) to the bases 

 of the arms ; the mouth is situated in the margin over the azygos 

 plates ; there is a small aperture, surrounded by an elevated border, 

 half-way between the mouth and the centre. ' I think this small 

 orifice is the anal aperture. 



This genus is distinguished from the genera Cyathocrinus and 

 Foteriocrinus by the depth to which the azygos inter-radials descend. 

 In these two genera they are always situated above the sub-radials ; 

 but in Carabocrinus one of them stands upon one of the basal plates. 

 The generic name is from the Greek Jcarabos, a crab. 



