BATOCRINID^. 531 



quite uniform; their upper and lower foces striated at the margin, and 

 smooth in the middle ; axial canal of moderate size. 



Homon and Locality. — In the Kinderhook group at 'Le Grand, Marshall 

 Co., Iowa, and in both divisions of the Burlington group at Burlington and 

 other places. 



Remarks. — There can be no doubt that the specimens of the three beds 

 represent one and the same species, although differing considerably in size. 

 In the Kinderhook group the specimens are smaller, and only a single dis- 

 tichal takes part in the calyx, while in the Burlington two or three of them 

 are incorporated, and the specimens have proportionally more interbrachial 

 plates. 



(?) Periechocrinus tenuidiscus (Hall). 

 Plate XL VL Fig. 4, and Plate LI. Fig. 6. 



1861. (?) Actimcrittus tenuidiscus — Hail; Prelim. Descr. New Grin., p. 14. 



1877. Actinocriniis teimidisais — S. A.. UaLET!.; Catal. Pala;oz. Foss., p. 68. 



1881. Feriechocmms tenuidiscus — "W . aud Sp. ; Revision Palffioer., Part 11., p. 133. 



Closely allied to the preceding species, and perhaps a mere variety of the 

 same. Dorsal cup more compressed, and distinctly rounded, the arm bases 

 less projecting, and the plates ornamented. The plates of the dorsal cup 

 covered by broad, ill-defined ridges passing out from near the middle of the 

 plates to the margins, where they meet the ridges of adjoining plates. The 

 ridges following the brachials more prominent, especially as they approach 

 the arm bases. A similar ridge follows the median line of the anal area. 

 The surface of the plates is beautifully marked by very fine radiating wrink- 

 les ; the plates very thin at their outer margins, and but little thicker in the 



middle. 



Basals forming a low hexagonal basin, with a slightly projecting rim at 

 the bottom; the column facet somewhat concave, occupying one half the 

 diameter of the cup. Radials large, nearly as long as wide ; the costals con- 

 siderably smaller, decreasing in size upwards in the same proportions as the 

 radials and first costals. Distichals, so far as observed, two or three in the 

 lyx ; the two upper ones curved like arm plates. First interbrachial as large 

 the first costals, and as wide as long, those of the second row equal to the 

 second costals ; the second row has two or three plates, and the succeeding 

 ones three or four. Anal interradius very wide ; the first anal plate smaller 

 than the radials; the three plates overlying it as large as the first inter- 



ca 

 as 



