528 THE CEINOIDEA CAMERATA OF KORTH AMERICA. 



upper ones together, tlie latter meeting the interambulacral pieces. Inter- 

 brachials apparently three. Ventral disk rather depressed near the outer 

 margin ; the central portions gradually rising to a good-sized anal tube, 

 composed of moderately large, convex plates similar to those forming the 

 tegmen. 



Horizon and Locality. — Niagara group ; Yellow Springs, 0., and St. Paul, 

 Shelby Co., Ind. 



.SCTZfwfe.-^ This species departs from the others in having a large anal 

 tube, a character which in other groups has been regarded of generic im- 

 portance, and we should propose for it a new genus if we were better 

 informed as to the anal structure of the other species. 



Periechocrinus tennesseensis (Hall). 

 Plate L. Fig. 4. 



1850. Saccoerinus tennesseensis — Teoost MS. 



1875. Saccoerinus tennesseensis — Hail; Geol. Eep. Olio, PaliEonf,., Vol. IT., p. 125, Plate 6, Fig. 10. 



Syn. Saccoerinus speciosus — Eoemek (not Hall) ; Silur. Fauna des West! Term., p. 42, Plate 3, 

 Figs. Sa, b, c. 



Of the type of P. spedosus Hall, but the third divi.sion of each ray takes 

 place in the calyx and not in the arms ; and it has twenty primary arms in 

 place of ten. Dorsal cup elongate obconical, one fourth higher than wide, 

 slightly inflated at two thirds its height. Arm bases conspicuously projecting, 

 deeply depressed between the rays and their main divisions ; the depressions 

 of the anal side widest and deepest. Surface of plates smooth, with a faint 

 longitudinal elevation along the radial series, which at the top of the dorsal 

 cup widens to the full width of the arms. 



Basals forming a somewhat conical cup. Eadials much larger than the 

 costals; the latter considerably narrower, and but little longer than wide. 

 Distichals two, half the size of the preceding axillary, as wide as high. Pal- 

 mars still smaller, rounded like arm plates. Arms thin, cylindrical, arranged 

 in pairs, biserial from their origin. Interbrachial areas composed of five or 

 six rows ; the plates arranged as in the preceding species, including those of 

 the anal side. Ventral disk constructed of a number of polygonal plates 

 •without definite arrangement. Anus subcentral. 



Horizon and Locality. — Niagara group ; Decatur and Perry Cos., Tenn., 

 and Yellow Springs, 0. 



Eemarks. — The type specimen, collected by Dr. Troost, came from De- 



