FOSSIL CRINOIDS. 1 29 



The anterior ray probably bifurcates higher than the others, as a rule. Dor- 

 sal canal extending throughout the arms (Fig. 12, where it may be seen toward 

 the distal end of the injured arms). Ventral furrow broad, roofed by two inter- 

 locking rows of covering plates, about 3 pairs to the ordinary brachial and 9 or 

 10 pairs to an axillary (Figs. 8 and 9, showing the plates and their sockets). 

 Infrabasal disk small, with obtusely quadrangular column facet, central axial 

 canal, and usually four smaller ones surrounding it. Anus relatively small, 

 and so far as observed not followed by any plate between the radials; Fig. 6a 

 looks as if there might have been one, but this is not certain, as the plates are 

 displaced. Column with highly projecting nodals and long internodes, as well 

 shown by Fig. ob. Surface smooth. 



Horizon and Locality. In rocks of the Onondaga formation, near Le Roy, 

 Livingston county. New York, associated with Myrtillocrinus and Schultzi- 

 crinus; it has not been found outside of that region. 



The calyx plates of this species are fairlj' thick,' but it is singular how rare 

 it is to find a specimen showing the structure of the infrabasal disk; Fig. 66 is 

 the only one out of numerous specimens that shows it plain enough to figure. 

 The beautiful specimen figured at 5a, 6, on Plate II, is in the New York State 

 Museum at Albany, as is also that of Fig. 7; the former is in a thin piece of 

 free shale, with the calyx and arms in relief on both sides, the stem showing 

 on one. Figs. 4a, h are from an equally characteristic and well preserved speci- 

 men in the American Museum of Natural History, New York; Fig. 3, from the 

 same collection, is the only one of Hall's types that can be identified, and it is 

 in poor preservation as to the caljTc, and apparently abnormal. The other 

 specimens figured are in my collection, the fruit of two seasons' careful searching 

 of the type region by Mr. Kirk. 



Akachnocrinus extensus Wachsmuth and Springer. 

 Plate I, figs. 1, 2, 3, 4; PI. II, figs. 1, 2. 



1879. Rev. Pal., I, 93. 



A large species, perfectly distinguished from .4. bulbosus by the absence of 

 any special enlargement of the axillary brachials; all brachials are very short 

 and wide in the lower part of the ray, about 1.5 to 5, deeply rounded but their 

 surface not convex, the axillaries only larger by the slope necessary to start 

 the divisions. Arms thick, round, long, branching three to five times. The 

 rays divide usually on about the third IBr (occasionally one or two less or more), 



