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, Wisc., and Chicago, Ills. 
Siphonocrinus nobilis (Hatt). 
Plate XIX. Figs. 1a, b, and 2a, b, ¢. 
1861. Glyptocrinus nobilis — Haut; Rep. Progr. Geol. Survey Wisc., p. 21; also 1867, 20th Rep. N. York 
State Cab. Nat. Hist., Plate 10, Figs. 9, 10. ‘ 
1881. (2) Glyptocrinus nobilis — W. and Sp.; Revision Paleocr., Part II., p. 189. 
1882. Glyptocrinus nobilis — Wutrr1eLD; Geol. Wisconsin, Vol. IV., p. 282, Plate 16, Figs. 9,10. 
1888. Siphonocrinus nobilis —S. A. MizteR; Amer. Geologist, Vol. I., No. 5, Fig. 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. Costals 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 
