1881. J NATURAL SCIENCES OF PHILADELPHIA. 2t3 



ary radials 2 to 4 x 1^? wider than high, supporting in direct 

 line a single rather stout arm or ten in all. It is possible that the 

 number of secondary radials varies with age, and that there are 

 four in the adult. 



Arms composed either of a single row of cuneiform plates 

 slightly interlocking, or of two rows of short plates alternately 

 arranged. 



Interradials four to eight ; the first large, resting upon the 

 sloping sides of the first radials and between the second and third 

 of adjacent ra3's, the succeeding plates much smaller and connect- 

 ing with the vault pieces. Posterior area wider ; the first anal 

 piece in line with the first interradials, the second and third 

 ranges consisting of two instead of three pieces. Anus in form 

 of a simple lateral opening similar to Dorycrinus. 



Vault compressed, conij)osed almost exclusively of the apical 

 dome plates, which are unusually large. In Stelidiocr. capitulum, 

 the vault is constructed of only twenty-three pieces, the smallest 

 possible number of which a species with ten arms can be composed 

 in accordance with the rule prevailing among these crinoids. It 

 consists of the central piece, the six proximal plates, a single anal, , 

 and three radials to each ray. The two secondary radials of the 

 dome are exceedingly small, while the proximal vault pieces 

 occupy almost three-fourths of the entire summit. 



Column round, articulating faces crenulated. 



The genus resembles PatelUocriyius , but differs from it and all 

 similar genera in the number of basal plates. 



Geological Position^ etc. — Restricted to the Upper Silurian of 

 Europe. 



We recognize the following species . — 



1878, Stelidiocrinus capitulum Angelin. Type of the genus. Iconogr. Crin. Suec., 

 p. 21, PI. 17, figs. 5a-g. Upper Silur. Gothland, Sweden. 



*1878. Stelidiocr. longimanus Angel. (Harmocr. longimanus). Iconogr. Crin, 

 Suec, PI. 21, figs. 6, 7. Upper Silur. Gothland, Sweden. 



1878. Stelidiocr. Isevis Angelin. Iconogr. Crin. Suec, p. 21, PI. 15, figs. 20, 20a; 

 also PI. 27, figs, 3, 3a, (not PI. 28, figs, 7, a, b). Upper Silur. Gothland, 

 Sweden. 

 Angelin's figures are not so reliable as could be wished. Those of S. Isemg on 

 PI. 15 have single jointed arms, while those on PI. 27 have a double series of 

 plates. It may be possible that the former are taken from a young specimen. 

 The figures 7 a b, on PI. 28 are evidently referred to this genus by oversight, , 

 as they are clearly of Desmidocrimis maerodactyhia, 



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