316 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



by broad, keel-like processes, which form into a knot in the centre of the 

 radials and second costals. Another prominent ridge runs from the lower 

 margins of the first interbrachials to the middle of the plates, where it forms 

 a rather sharp node, from which two branches proceed to the upper lateral 

 margins. The smaller ridges, of which there are three to four to each side, 

 are marginal, extending but a short distance into the plates. 



Basals small, perfectly anchylosed, surrounded by a circular ridge, and 

 entirely covered by the column. Radials larger than the costals, hexagonal, 

 wider than long, widest above the middle and not visible from a side view. 

 First costals short, quadrangular; the second considerably wider, a little 

 longer and axillary, giving off to one side an axillary distichal, which sup- 

 ports a small palmar at each side, and this an arm. The opposite distichal 

 gives off a single arm from the second plate, thus making three primary arms 

 to the ray. Arm bases projecting, giving to the calyx, as seen from above, 

 a pentagonal outline. Structure of the arms unknown. Interbrachials : 1, 1, 

 3; the first large; the second much wider than high; the middle plate of the 

 third row comparatively large ; the two at the sides as long, but narrower. 

 Yentral disk composed of but few large plates, which are covered with several 

 minute pustules of irregular arrangement ; the interambulacral spaces 

 depressed, consisting generally of only two plates, which abut against the 

 orals. There are no interdistichals. Orals and ambulacral plates arranged 

 as in the preceding species. Anus subcentral. 



Horizon and Locality. — Hamilton group; near Thedford, Ontario. 



Type in the Canada Survey Museum at Ottawa. 



Remarks. — It is barely possible that Hall's Cacabocrinus Troosti, from 

 Western New York, is identical with this species, but it is described with 

 four primary arms instead of three. 



Dolatocrinus triadactylus Baeris. 

 Plate XXVI. Figs 4a-d. 



1884. Babris; Proceed. Davenp. Acad. Nat. Sciences, Yol. IV., Plate 3, figs. 5-7, 



1885. W. and Sp. ; Eevision Pal^eocr., Part III., p. 105. 



Of medium size. Calyx depressed, a little wider than high. Dorsal cup 

 broadly basin-shaped ; the lower portions truncate to near the top of the 

 first costals, then curving rapidly upwards, a little constricted below the arm 

 bases ; the basals moderately excavated, and the margin of the cavity 



