298 SMITHSONIAN INSTITUTION 



Clidochirus americanus n. sp. 



Plate XXXVII, figs. 7-8 



A small species. Crown elongate pyriform, height to width at upper IIBr 

 about 1 to 1 ; spread of calyx from base to same level, 1 to 2.6. Surface smooth. 

 Maximum crown 25 mm. high by 15 mm. wide at upper IIBr; base 3 mm. 



IBB visible in pentagonal outline. BB small. RA much smaller than RR 

 in other rays. Anal x alone, angular above. IIBr 3 as a rule; IIIBr 4 or more; 

 one more bifurcation visible. Brachials not more than twice as wide as high, 

 evenly curved, without median ridges, tapering rapidly- above IIBr. Column 

 small, not expanding at top. 



This species is founded on two specimens from the top of the Medinan group of Ohio, 

 a horizon below that of the shales of Indiana and New York, and perhaps corresponding to a 

 horizon lower than beds c and d in which the Gotland species occur. It is a slightly more 

 elongate form than C. pyrum, as the proportionate dimensions averaged from all the speci- 

 mens show, and the brachials are proportionately longer and narrower. The size is about 

 the same as the average of that species leaving out the very large specimens. The difference 

 in size of the radianal between the two species is quite remarkable, and seems to be constant. 

 In this one it has the appearance of a reduced or undeveloped plate, much like that in some 

 specimens of Ichthyocrinus; here also the succeeding radial is somewhat ill-formed. The 

 brachials throughout are proportionally longer than in either of the other species, producing 

 greater elongation of the crown, even where the others have a larger number of plates 

 between the bifurcations. 



The stem, as shown in the largest specimen (PL XXXVII, fig. 8), has a little different 

 aspect from that of the Gotland specimens, being narrower in the proximal part, and the 

 joints further down more rounded. It shows a marked alternation of short and long 

 columnals diminishing distally until only the longer ones are left. The surface in both 

 specimens is imperfectly preserved, and they show no trace of the characteristic ornamenta- 

 tion of the type specimen of C. pyrum. 



No other specimens have been found besides the two figured. 



Type. Author's collection. 



Horizon and locality. Silurian, Brassfield formation at the top of the Medinan group ; 

 Dayton, Ohio. 



Clidochirus keyserensis n. sp. 



Plate XXXVII, figs, p-11 



A medium sized species. Crown angular, broadly rounded below, expand- 

 ing rapidly from base; base small. Height to width at IIBr 3 , 1 to 2.3 ; spread of 

 calyx from base to IAx, 1 to 4; cross-section at IIBr decagonal, with deep de- 

 pressions at the interbrachial sutures. Brachials thick, highly curved and 

 sometimes angular; transverse sutures strongly indented. Surface without 

 ornament. Maximum crown, 33 mm. high by 22 mm. wide at top of IIBr 3 . 

 Base at column facet, 5 mm. 



IBB very small, invisible beyond the column. BB small for the genus, 

 touching the column, and lying so flat as to be but slightly visible in a side view; 

 post. B supporting a narrow anal series of three or more plates. RA similar to 

 R in other rays. Br not only highly arched longitudinally, but strongly sloping" 

 to the proximal and distal margins, leaving deep, angular depressions at the 



