274 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



fourth and fifth plates (none from the third), which are long, but not as 

 conspicuous as in the preceding species, and they grow more obscure with 

 age. All brachials of the third order are free ; the two or three lower ones 

 are longer and have parallel upper and lower faces ; the others being short 

 and cuneiform. The arms, which branch once, are long, very slender, 

 rounded on the back, and provided with rather long pinnules. Interbrachial 

 plates large, to the fifth row nearly of equal size, and as large as the second 

 distichals ; arranged : 1, 2, 2, 2, 2. From the sixth row, where the pinnules 

 come in contact with the interbrachials, the arrangement is less regular, and 

 the plates gradually grow smaller. There seems to be no anal ridge, but the 

 posterior interradius has three plates in the third row, and frequently in the 

 second. The interdistichal spaces are remarkable for their great length, and 

 the large size of the plates; they are arranged: 1, 1, 2, 2, 3. Construction 

 of ventral disk, and position of anal opening unknown. Column round, 

 composed of short, sharply edged joints. 



Horizon and Localit?/. — Trenton limestone ; Ottawa, Canada. 



T^pes in the Canada Survey Museum. 



GlyptOCrinus ornatUS Billings. 

 Plate XX, Figs. 6a, h. 



1857- Billings; Geol. Siirv. of Canada (Rep. of Progress), p. 260; also 1859, ibid., Decade IV., p. 60, 



Plate 9, Pigs. 2a, h. 

 1881. W. and Sp. ; Revision Palfeocr., Part II., p. 189. 

 1883. S. A. Miller; Journ. Cincin. Soc. Nat. Hist., Vol. VI., p. 225. 



Of the type of Glyptocrinus Dyeri, but readily distinguished by its orna- 

 mentation, the smaller number of interbrachial and anal plates, and by 

 having ten arms instead of twenty. Calyx globose, the plates delicate, orna- 

 mented with five or six rather conspicuous, finely striated ridges, radiating 

 from the centre of the plates. The ridges passing up the radial and anal 

 plates are more prominent and broader than the others ; those from the 

 interbrachials, which are not confluent with the ridges of adjoining plates, 

 forming a well defined star upon each plate. 



Base short, with a projecting rim and a shallow depression at the bottom. 

 Radials and costals a little wider than long, the radials one third the largest. 

 Four of the distichals generally take part in the calyx, of which the two 

 proximal ones are nearly as large as the upper costal, the second pinnule- 

 bearing ; the two succeeding ones are much smaller, but yet twice as large 



