50 University Geological Survey of Kansas. 



close together ; each of the two series is apparently separated 

 by a row or two of imperforate plates at the ambitus. Both 

 series are in contact at the apex and near the mouth. Number 

 of columns of interambulacral plates unknown, but apparently 

 about three. The ambulacral area is very wide and the two 

 series are widely separated at the ambitus. Some of the inter- 

 ambulacral plates seem to be pierced by a single pore, or, some- 

 times, two. Indistinct elevations seem to be present in three 

 columns, one of large and two of small size. 



Diameter of specimen 23 mm. 



Maximum diameter of ambulacral area 6 



Maximum diameter of each series 2 



Maximum diameter of interambulacral area 7 



Pores distant in vertical rows § 



Pores distant in the same series lo 



Pores distant in single pair \ 



Range and distribution : Upper Coal Measures ; collected 

 from the Deer Creek limestone, near Topeka. 



The specimen is badly worn and somewhat compressed ; the 

 surface markings are almost entirely removed. It agrees to 

 some extent with Oligoporus, but the ambulacra are divided into 

 two series with, apparently, two columns of imperforate plates 

 between them. However, this is not unquestionably shown by 

 this specimen. It will, in all probability, be found to belong to 

 an entirely different genus. It is referred to Oligoporus for con- 

 venience, until better material can be secured. It does not 

 seem to present the appearance of any other Carboniferous sea- 

 urchin with which I am acquainted. 



