212 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



which crosses the mouth, overlies the upper part of the anterior ambulacra, 

 and is continued subtegminally all the way to the anterior side of the calyx, 

 even beyond the arm regions, where it bends outward. The ambulacra, as 

 seen from the converging ridges upon the casts, vary considerably in length 

 in some of the rays, the posterior ones being much longer, especially those 

 to the left, which are quite conspicuously displaced. The excentric position 

 of the mouth, and the irregular arrangement of the ambulacra of this species 

 remind us of the Comatulid genus Actinometra. 



Horizon and Locality. — Upper part of Niagara group ; Racine, Green- 

 field and Waukesha, Wise, and Chicago, Ills. 



Siphonocrinus nobilis (Hall). 

 Plate XIX. Figs, la, h, and 2a, h, c. 



1861. Glypiocrinus nohilis — Hall ; Rep. Progr. Geol. SuiTey Wise, p. 21 ; also 1867, 20th Rep. N. York 

 State Cab. Nat. Hist., Plate 10, Pigs. 9, 10. 



1881. (?) Glyptocrinus nobilis — W. and Sp. ; Revision Palseocr., Part II., p. 189. 



1882. Gly]ptocTi7ms ;^o/^^7^> — Whitfield ; Geol. Wisconsin, Vol. IV., p. 282, Plate 16, Pigs. 9, 10. 

 1888. Siphonocrinus nobilis — S. A. Miller; Amer. Geologist, Vol. I., No. 5, Pig. 265. 



Calyx as large as in the preceding species, and of similar form ; but the 

 ventral disk proportionally higher, and the anal tube directed upwards, not 

 being conducted subtegminally to the anterior side of the calyx. The orna- 

 mentation — as observed in gutta percha casts taken from natural moulds 

 in the rock — is characterized by sharp radiating ridges, passing from the 

 centre of each plate to adjoining ones, and presenting upon the surface 

 of each a well defined stellate figure with a slight elevation in the centre. 

 A similar style of ornamentation, but less distinct, occurs upon the plates of 

 the disk and anal tube. 



Infrabasals and basals as in S, armosus ; the latter with sharp upper 

 angles reaching far up between the radials, and sometimes meeting the first 

 interbrachials. Coatals smaller than the radials. Distichals three, large; 

 succeeded by several palmars, which are but little larger than good sized 

 arm plates. There are four arm openings to the ray, arranged in pairs, 

 with a shallow depression between each pair, and a somewhat wider and 

 deeper one between the pairs of different rays, the latter extending quite 

 a distance into the ventral surface, and forming deep grooves along the 

 margin. Arm structure unknown. Interbrachials : 1, 2, 2, 2, 3 ; succeeded 

 in the disk by comparatively large, less regularly arranged plates, which 



