MELOCRINID^. 279 



A small species. Dorsal cup obconical with slightly convex sides ; 

 section across the costals sharply pentagonal, owing to the conspicuous radial 

 ridges, which pass from the arms down to the centre of the radials, where 

 they divide and are continued to the basals. The ridges, which are rounded, 

 grow narrower toward the middle of the plates, widening at their margins. 

 Surface, except along the ridges, covered with numerous small pustules 

 without definite arrangement. 



Basals large, forming a pentagonal cup with a rim around the bottom. 

 Eadials twice or nearly three times as large as the second costals ; the first 

 costal larger than the second. Distichals free beyond the fourth plate ; the 

 first and second considerably the larger j the second one pinnule-bearing, 

 and also the fourth (not the third), which is slightly wedge-shaped, and con- 

 siderably smaller than the preceding ones ; from the fifth to the eighth, the 

 plates are decidedly cuneate, the higher ones interlocking. Arms 10, simple 

 throughout; thin, composed of two series of trigonal pieces. Interbrachials : 

 1, 2, 2, etc.; the plates large. Anal side slightly wider; the first plate 

 a little larger than the corresponding ones of the other sides ; the succeed- 

 ing pieces comparatively smaller ; there are three plates in the second row, 

 and in all the rows above. The plates of the median series are formed into 

 a conspicuous longitudinal ridge, which divides on the first anal plate, send- 

 ing a branch to the middle of adjacent radials. Nothing is known of the 

 structure of the ventral disk and anal opening, and nothing definitely of the 

 column. 



Horizon and Locality. — Black River limestone ; Renfrew Co., Canada. 



Tyjpe in the Canada Survey Museum at Ottawa. 



BemarJcs. — The large columns which E. Billings figures from the Tren- 

 ton group of Ottawa, and which he thought might be referable to G. priscus, 

 probably belong to a different species. 



STELIDIOCRINUS Angelin (Eestricted by W. and Sp.). 



1878. Angelin; Iconogr. Crinoid. Suec, p. 21. 



1879. Zittel; Handb. der Palgeont., Vol. I.,p. 345. 



1881. W. and Sp. ; Revision Palaocr , Part II., p. 98 (Proceed. Acad. Nat. Sci. Pliila., p. 272). 

 1885. VT. and Sp. ; ibid., Part III., p. 103 (Proceed, p. 324). 



Calyx small, subturbinate, plates smooth; interradial areas depressed; 

 radial plates elevated but not ridged; ventral disk composed of but few 

 plates. 



