342 PALAEONTOLOGY OF ILLINOIS. 



of from eight to ten simple joints, the first joint one-half higher 

 than wide, and differing from the others by being flattened at the 

 dorsal side, all succeeding ones rounded at the outer side, with 

 slightly expanded ends ; upper and lower sides almost parallel. The 

 length of the joints is somewhat irregular, varying from three to 

 four times their width, but in proportion to the width of the arm; 

 ventral groove wide and deep. No pinnules have been observed, and 

 the construction of the vault is unknown. 



Column circular very strong at the basal disk, but tapering so 

 rapidly in its course downward that at about one-fourth of an inch 

 it is reduced to less than one-third its greatest width, whence it re- 

 mains stationary as far as it is preserved in the specimen. The 

 segments of the upper or conical part are short, sharply edged, and 

 of the same height, but as soon as the column attains its ordinary 

 size, the joints become abruptly higher, more cylindrical, and thicker 

 and thinner joints alternate in the usual way. Central perforation 

 small. 



The specific name is given in honor of P. Herbert Carpenter, 

 Assistant Master at Eaton College, England, one of the founders of 

 the genus Allagecrinus* 



Geological position, etc: From the Chester or Kaskaskia limestone, 

 Monroe county, Illinois. 



Illinois State collection. 



*The genus was proposed by P. Herb. Carpenter and Dr. R. Etheridge, jun., for a 

 small species from the Carboniferous of Scotland. [Annals and Magazine Nat. Hist., 

 April 1881, p. 281. 



