ACTINOCRINID^. 563 



fourth row extending far out on the brachial extensions. There are numer- 

 ous other interradial plates above, but these take part in the tegmen. The 

 anal piece supports two plates in the first row, two in the second, and 

 numerous other plates above. Ventral disk depressed convex, somewhat 

 bulging above the rays ; the orals and ambulacral plates sharply nodose ; 

 the interambulacrals almost flat. The orals are not in contact, being separ- 

 ated by small, flat pieces. Ambulacral plates arranged in alternate rows, 

 which bifurcate from a large axillary, and form secondary and tertiary rows 

 toward the arms. Anal tube nearly central. 



Horizon and Locality. — Keokuk group ; Keokuk, Iowa, and other places 

 in Missouri and Illinois. 



Actinocrinus jugosus Hall. 

 Plate LIV. Fig. 1. 



I860. Hall; Suppl. Geol. Rep. Iowa, p. 49. 



1881. "W. and Si?. ; Revision Palffiocr., Part II., p. 144 



A large species, also always found in a crushed condition, so that its 

 form cannot be accurately ascertained. It seems to be nearest to A. Loivei, 

 which it resembles in the mode of ornamentation, but from appearances the 

 calyx is more elongate, the plates thinner and more evenly proportioned, 

 the brachial extensions less prominent, the interbrachial space.s considerably 

 narrower, and the higher brachials of the calyx much shorter and smaller 

 generally, indicating also that the arms were much thinner. Plates convex, 

 traversed by ridges which meet in nodes at the centres ; the nodes of the 

 radials, costals, distichals and anal plate transverse, those of the inter- 

 brachials round. From those of the radials four ridges pass down to the 

 basals, three others upward to the first costals, and sometimes the same 

 number runs to the second costals, but there is never more than one ridge 

 between the other plates. 



Basals forming a wide cup, with a slightly projecting, smooth collar at 

 the lower end, and deeply grooved at the interbasal sutures. Eadials and 

 both costals longer than wide ; the latter about one half the size of the 

 radials. Distichals a little smaller than the costals, nearly as long as wide, 

 and all axillary, giving off an arm to one side, and two palmars to the other. 

 The two lower fixed arm plates are nodose, as wide as long, and as large as 

 the palmars of the opposite side, of which the second is axillary, and gives 



