8 



an inch in length. Oral, genital and ocular plates unknown. 

 The form of our fragment indicates a length greater than the 

 diameter, but as this is different from the form of all other 

 species, it cannot be asserted any stronger than the appearance 

 shown by the illustration. 



The interambulacral areas are elongate-lance-elliptical, in out- 

 line, and moderately convex transversely. There are only four 

 ranges of plates at the middle part, and they extend almost to 

 the summit, where one terminates, and the other three continue 

 to the genital plates. 



The ambulacral areas are nearly as wide in the middle part, 

 as the interambulacral areas, and they are of almost uniform 

 width throughout their length, slowly tapering as they approach 

 the summit and ocular plates. They are separated in each am- 

 bulacral field by a sharply defined ridge, elevated higher than 

 the interambulacral areas. The plates are short and small in 

 the ambulacral depressions and each one is pierced with a pair 

 of circular pores. There are two ranges of these ambulacral 

 pores in each depression throughout the length, without the ad- 

 dition or intercalation of any plates or pores. 



This species is distinguished from all others by its general 

 form and by having only four ranges of plates in the interam- 

 bulacral areas. 



Found in the Keokuk Group, at Boonville, Missouri, and now 

 in the collection of Wm. F. E. Guiiey. 



OLIGOPORUS SULCATUS, n. Sp. 



Plate I., Fig. 4, basal view; Fig. 5. apical view. 



Our specimen with the exception of the loss of a few plates is 

 quite complete. It is silicified and not compressed in any direc- 

 tion, most of the sutures are more or less destroyed, but the 

 outlines of some of the plates are preserved, and where the 

 plates are broken wholly away, the cast shows the bases of the 

 plates distinctly. The lower half has more of the plates broken 

 away and shows the pores of the ambulacral areas better than 

 the other half. The mouth, ocular, genital and anal plates are 

 not preserved, with the exception of one ocular and two genital 

 plates, that may be distinguished. 



