15 



wide as high, the arm facets occupying more than half the width of 

 the plates, shallow and somewhat protruding below ; second, third, 

 fourth and fifth radials small, about as wide as high, subcylindrical, 

 except the fifth, which is pentangular in outline, and upon which the 

 arms bifurcate, which are composed of a single series of joints with 

 parallel sutures ; arms not large, and apparently ten in number. 



Surface smooth, or finely granulose. 



Four specimens, more or less perfect, of this species have been dis- 

 covered, presenting very constant characters. 



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

 stone, Burlington, Iowa. — Cabinets of B. J. Hall, Esq., and Rev. W. 

 H. B arris. 



Genus AcTiNOCRiisrus Miller. 



AcTiNOCRiNUS QUADRisPiNUS (n. s.) Body small, flat below, the 

 rays passing out horizontally ; basal plates nearly as large as the first 

 radials, slightly depressed in the centre for the attachment of the 

 column ; first radials hexagonal and heptagonal, wider than long ; 

 second radials a little shorter than the first, but reaching the outer 

 part of the body, and much bent upward at the sides to meet the 

 inter-radial plates, and to conform to the convexity of the under side 

 of the projecting part of the rays, wliich are broken off in our speci- 

 men ; inter-radi^l series consisting of three plates, the largest below 

 which is hexagonal, and supports the other two; anal series consist- 

 ing of seven plates, the first about the size of the first radials, the 

 others smaller, in two arching rows of three abreast. Dome much 

 elevated, composed of very numerous small plates, and surmounted 

 by a strong, tumid plate at the apex, which is surrounded by four 

 -adjacent, short, strong, diverging spines, situated directly over each 

 inter-radial space, and by a comparatively large proboscis which 

 passes up from the anal side, all of which adjoin the summit plate ; 

 the anal space and proboscis being proportionally broad, the spines 

 occupy but little more than the anterior half of the summit of the 

 dome. 



This species approaches A. planohasalis and A. injiatus of Hall, 

 but differs from them in its general form, the arrangement of the 

 plates, the four summit spines and side proboscis. 



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

 stone, Burlington, Iowa. — Collection of Mr. Charles Wachsmuth. 



AcTiNOCKiNUS Wachsmuthi* (u. s.) Body somewhat pentalobate 

 in outline at the arm bases ; broadly spreading from the base, which is 

 small ; basal plates rather short, but projecting downward, forming a 

 rim around the column, which is notched at the sutures ; cicatrix for 



*Mr. Charles Wachsmuth, Burlington, Iowa. 



