360 PALEONTOLOGY OF ILLINOIS. 



Column of medium size, round, composed at the upper end of 

 high joints. 



The ornamentation of the radials consists of indistinct concentric 

 curves sub-parallel with the arched upper surface of the plate. 

 The ornamentation of the oral plates, as in most species of Elwa- 

 crlnus, is sharply divided by two longitudinal lines, the median part 

 (which in position and somewhat in form, at the four lateral sides 

 of the body, corresponds to the large anal plate of the posterior 

 side) is more or less destitute of ornament. The two sides, how- 

 ever, are crowded with rows of small granules, arranged so as to 

 divide the field into narrow parallel spaces, which are transversely 

 arranged, and of the width of the pore-pieces. 



Observations. Elccacrinus obovatus differs from Eloeacrinus (Nucleo- 

 crinus) angularis, Lyon, in the greater length of the body, and in 

 having straight and not concave sides. It resembles, perhaps, 

 closest Elaeacrinus (Nucleocrinus) lucina Hall, and may be identical 

 with the larger form noticed in the same paper, and which Hall consid- 

 ered a variety or more adult phase of the above species. Hall de- 

 scribes the latter as more expanded in the upper part of the body, 

 with the base proportionally narrower, and this agrees with our 

 species ; but the body is comparatively longer than in Hall's smaller 

 type ; while it should, if representing the adult form of the other, 

 (according to Wachsmuth; see the preceding paper), on the con- 

 trary be wider and not higher. In Elceacrinus lucina the basals are 

 almost on a plane with the radials, and the ambulacra touch the 

 bottom, which is not the case in E. obovatus ; in the former the 

 lower truncate portions are much wider, and the basals instead of 

 being deeply concave, are provided with an elongate node in the 

 center. 



The above description was made from ten specimens of all sizes, 

 the largest one measuring one inch and three quarters in length, 

 the smallest seven-eighths of an inch. 



Geological position, etc.: Found in the shales of the Hamilton 

 group at Buffalo, in limestone of the same age at Iowa City, and 

 at the top of the Hamilton group in the Thunder Bay region of 

 Northern Michigan. 



The original specimens are in the collection of Mr. Charles Wachs- 

 muth and in my own. 



