THYSANOCRINID^. 195 



sides of the ridge, small radiating lines pass out to the interbrachials, form- 

 ing triangles of whieh the intervening spaces are granular or covered with 

 fine striations. Stronger ridges pass from the radials to adjoining basals, 

 where two of them meet, and proceed as a single ridge to the infrabasals. 

 The latter ridges form around the column a sharply defined pentagon, whose 

 salient angles lie in a radial direction. 



Infrabasals of moderate size, forming a narrow belt around the column, 

 which is visible in a side view. Basals large, without nodes, rapidly spread- 

 ing. Eadials larger than the costals, second costals narrower than the first. 

 Arms apparently ten, of which in mature specimens the six or seven lower 

 plates are incorporated ; arm plates comparatively large, elongate, and 

 slightly wedge-form. Interbrachial plates large ; arranged : 1, 2, 3, 3, with 

 a fifth row at the level of the arm bases. Anal interradius considerably 

 wider, having three plates in the second row, and four in the third ; — there 

 being no continuous row of anal plates or any sort of elevation. Interdis- 

 tichals five to seven. Ventral disk unknown. Column round ; axial canal of 

 moderate size ; pentalobate, the lobes directed radially. 



Horizon and Locality. — Niagara group ; Waldron and Hartsville, Ind. 



Types in the American Museum Natural History, New York. 



RemarJcs, — This species differs from Thysanocrinus inornatus in the larger 

 size of the infrabasals, the arrangement of the plates of the anal side, the 

 absence of an anal ridge, and in the general ornamentation of the plates. 



Gly piaster occidentalis (var.) increbescens is, in our opinion, not sufiiciently 

 distinct to be ranked as a variety. 



Thysanocrinus brachiatus Hall. 

 Plate XVIII. Fig. 7. 



1852. Olyptaster bracMatm — 'Rajsl ; Palseoiit. N. York, Vol. II., p. 187, Plate 41, Fig. 4. 

 1881. Ghjptaster brachiatus — 1^. and Sp. ; Revision Palaeocr., Part IL, p. 196 (Proceed. Acad Nat. Sci 

 Phila., p. 370). 



Calyx subglobose, having very strong radial ridges which bifurcate at 

 both ends. The lower branches proceed to the basals, and produce a well 

 defined pentagon, subdivided into fiYQ nearly equal fields by another row of 

 ridges; the upper branches follow the distichals, and pass into the arms. 

 The general surface without ornamentation. 



Infrabasals small, but exposed beyond the column, and visible even in 

 a side view. Basals of moderate size. Radials deeply notched for the 



