526 THE CEINOIDEA CAMERATA OF NORTH AMERICA. 



est width about one fourth its height; succeeding pktes in rows of two, the 

 upper ones small and irregularly arranged. Anal interradius wide, de- 

 pressed between the arm bases, and forming at the ventral surface a rounded 

 ridge, which connects with the anus ; the plates very numerous and irregu- 

 larly arranged. Interdistichals generally 1, 2, 2. A^entral disk low-con^-ex, 

 the interambulacral spaces depressed, the plates nearly flat. The food 

 grooves in the cast are delineated by prominent ridges, which bifurcate half 

 way out to the arms, and again close to the arm bases, giving off in the 

 calyx four arms to the ray. 



Horison and Locality. — Upper part of Niagara group, near Chicago, Ills. 



EemarJcs. — This species was regarded by Hall as a synonym of Periecho- 

 crinus Whitfieldi, but we agree with Miller that the two forms are distinct. 

 The plates of P. Whitfeldi are flat and finely ornamented, those of P. infdix 

 convex and without ornamentation ; the radials of the former possess promi- 

 nent ridges, which are wanting in the other. We disagree with Miller, 

 however, as to his " Saccocrinus" JEgani, which we take to be identical with 

 P. infelix. 



Periechocrinus urniformis (S. A. Miller). 

 Plate L. Figs. 5a, b. 



1S81. Saccocnnus ■urniformis — S. A. Millek; Journ. Ciucin. Soc. Nat. Hist., Vol. IV., p. 170, Plate 4, 



Figs. 2, 2«. 

 1885. FeriechocriTius urniformis (?) — "W. and Sp. ; Revision Pala^ocr., Part HI., p. 106. 



SjQ. Saccocriniis pjriformis — S. A. Millee; 1882, Journ. Ciucin. Soc. Nat. Hist., Vol. T., p. 81, 



Plate 3, Fig. 3. 

 Syn. Periechocrinus pi/riformis (?) — W. and Sp. ; Revision Palseocr., Part III., p. 106. 



Only known from internal casts. Calyx large, ovoid ; greatest width 

 across tlie arm bases, which are somewhat projecting ; jjlates gradually 

 decreasing in width upwards. 



Basals small, forming a rather low cup. Eadials and costals nearly of 

 equal size ; their width across the middle equal to their height ; the upper 

 and lower faces less constricted than in the preceding species. Distichals 

 two, the first one fourth, and the second as much as one half, smaller than 

 the costal axillaries. Palmars two, small. Interbrachial and interdistichal 

 areas on a level with surrounding brachials, except close to the arm bases, 

 ■where they form rather wide, well marked depressions, which are continued 

 upon the tegmen. First interbrachial of about the same size as the first costal, 

 but pentangular in place of hexangular; succeeded by six to seven rows of 



