20 



gentle curves to the arms, about one-third higher than wide ; base about 

 one-third the height of the body, truncated and shghtly excavated for 

 the attachment of the column which is round and moderately small ; 

 lateral first radials about twice as high as wide, sides nearly parallel, 

 or a little narrower at the lower ends, which are slightly rounded ; anal 

 and anterior first radial plates wider below than above, their lower 

 ends angular, fitting into the retreating angles at the sutures of the 

 b'se; arm-facets shallow, narrow, and occupy the greater part of the 

 width of the plates ; second radials very short, scarcely reaching so high 

 as the tops of the first radials ; third radials also very short ; upon 

 these the arms rest, being composed of two short plates, each, when they 

 bifurcate, and are continued to the ends by a single series of short 

 plates with parallel sutures, giving twenty arms in all, which are about 

 twice the length of the body, and very small. A strong proboscis ex- 

 tends far up within the arms, based upon the large anal plate. Plates 

 of the body smooth, or finely granulose. 



This species differs from all others with which it is associated in the 

 thickness of its plates ; other marked peculiarities are its small arms, 

 very short second and third radials, and strong proboscis. 



Locality and position, in the upper division of the Burlington Lime- 

 stone, Burlington, Iowa. — Collections of Eev. W. H. Barris and Mr. 

 Charles Wachsmuth. 



Penteemites Sieius (summit view) twice enlarged. 

 Genus Pentremites Say. 

 Penteemites sirius (n. s.) Body depressed turbinate, pentagonal 

 in outline, looking down on the summit, which is broadly convex to the 

 sides, from which it slopes abruptly to the base ; this is narrow, and 

 has a small truncation for the attachment of the column ; basal plates 

 proportionally high; radials longer than wide, but are much bent, 

 following the shape of the body ; ambulacrals are as narrow, extending 

 outward from the body in a horizontal direction, their full length from 

 the summit being about equal to the transverse diameter of the body, 

 leaving about half of their length projecting from the sides, and are 



