102 



Cincinnati Society of Natural History. 



canal rather large. (Canadian Organic Remains, Decade 4, 

 1859, p. 63 ; Wachsmuth & Springer, Review of Palseocrin- 

 oidea, Pt. II, 1881, p. 192.) 



Remarks. — Originally described by Billings, this genus was 

 redescribed by Wachsmuth and Springer in 1881, and this 

 amended description is given above. Various changes have 

 been made from time to time in the species referred to the 

 genus, but at present those given below are the ones gener- 

 ally recognized as belonging to it from our region. 



1. — R. o'nkai^i Hall, 1866. 



Calyx turbinate, gradually spreading from the base to the 

 free arms ; deeply pentalobate below the third radial plates, 

 from the depression of the interradial space ; ten lobed above 

 from the depression of the intersupraradial areas ; imder-basals 

 well developed but small, and presenting a low, triangular 

 face on the exterior with very slightly truncated lateral 

 angles; basals larger, heptagonal, height and width about 

 equal ; upper extremities truncated by the interradial and 

 anal plates ; primary radials subequal in size, the first and 

 third having a general pentagonal form, and the second 

 quadrangular; siipraradial series, consisting of 14 to 16 

 plates — sometimes less — large in the lower part, becoming 

 gradually smaller above, the upper ones about five times as 

 wide as high ; the lower plates attached to the calyx and dome 

 by the intersupraradial and summit plates, while the upper, 

 smaller plates are free and bear tentacles ; interradial and 

 anal plates very numerous ; those of the middle range pass- 

 ing from the basal plate upward are largest ; the plates 

 between these and the row are small, some of them minute ; 

 anal area with 50 to 60 plates ; 40 to 50 in the interradial, 

 and 20 or more in the intersupraradial ; arms 20, composed 

 of a single series of very short plates, higher on one side than 

 on the other, but bearing tentacles on the longer side only; 

 tentacles long and slender ; surface of radial plates marked by 

 an elevated, rounded ridge, which bifurcates on the first and 

 third radials, the branches passing to the basals and thence 

 to the under basals; no other surface marking seems to have 



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