522 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



those of the intervening joints angular ; the axial canal rather large and 

 circular. 



Horizon and Locality. — Niagara group, above the shales ; Lockport, N. Y. 



Types in the American Museum at Nev? York. 



RennarTts. — P. speciosus, which was made by Hall the type of Saccocrinus, 

 is the only known American Periechocrinus in which the second bifurcation 

 takes place in the arms. 



Periecliocrinus Whitfieldi (Hall). 

 Plate LI. Figs. 1, 2a, h, 3, 4. 



1863. Aciinocrinus Ckristi/i — Hall; Trans. Alb. Inst., Vol. IV., p. 196. (Abstr., p. 2), not Actixocrinus 



Christi/i Slmm., 1865. 

 1868. Actinocrimts TF/ii/Jieldi — 'EkLL i^Oth. Rep. N. Y. State Cab. Nat. Hist. (Doc. Edit.), p. 326. 

 1863. Saccocrimis Christi/i — Meek and Worthen; Geol. Hep. Illinois, Vol. HI., p. 347, Plate 5, Fig. 1. 

 1870. Actiiiocrims (Saccocrinus) Whitficldi—'B.i^i,; 20tli Eep. N. Y. State Cab. Nat. Hist. (Revised 



Ed.), pp. 370 and 430. 

 1877. Saccocrinus Christiji — S. A. Millee; Catal. Amer. Palasoz. Foss., p. 90. 

 1879. Saccocrinus Ckrisli/i — B.f.i.L; 28tli Rep. N. Y. State Cab. Nat. Hist. (Revised Ed.), p. 127, Plale 



13, Figs. 12-20. 

 1881. Periechocrinus Chrisiyi — W. and Sp. ; Revision Palaeocr., Part H., p. 132. 

 1881. Saecocriims C/iristyi — Ball; lltli Ann. Rep. Indiana, p. 254, Plate 12, Figs. 12-20, Plate 15, 



Figs. 3, i. 



A moderately large species. Calyx subovate ; the dorsal cup lu-n-shaped, 

 its sides convex and but slightly spreading below the arm bases ; the ventral 

 disk low hemispherical, the plates thin and flat, the radial ridge proceeding 

 from the middle of the radials to the arms rather obscure. Surface of plates 

 finely granulose, the granules arranged in excentric lines, parallel to the 

 margins of tlie plates. 



Basals large, more rapidly spreading than the succeeding plates. Eadials 

 and costals decreasing in size upwards ; the radials nearly three times as 

 large as the second costals, and longer than wide, the upper and lower faces 

 much smaller than any of the others. Distichals two, of the size of the sec- 

 ond costals, supporting two or three .small palmars, which are succeeded by 

 the arms, the structure of which is not known. Interbrachials : 1, 2, 2, 2, 

 sometimes with a sixth row within the arm regions ; the plates, as a rule, 

 are longer than wide, and agree in size with adjoining brachials. Interdis- 

 tichals 1, 2, 2 ; the lower one larger, resting between the first distichals. 

 Anal interradius very wide ; the anal plate of equal width with the radials, 

 but not quite as long ; the three plates of the second row longer than wide ; 

 the middle plate the narrowest ; the third row also consists of three plates. 



