490 PAljEONTOLOGICAL report op geological survey. 



specimens, are separated from the pieces on either side of thepseudam- 

 bulacrse, by a sharply defined angular ridge, surrounding the whole 

 piece except at the junction with the branches of the radials below it. 



Anal piece. This piece is wider than the interradial pieces ; nearly 

 equal in width in its whole length; rounded at its summit, having a circu- 

 lar notch in its upper margin, the sides of which are frequently trunca- 

 ted obliquely downward from the sides of the notch, above which is 

 situated the large ovoid opehiag. It rises from the Summits of the 

 second radials, like the interradial pieces, and like those it is marked 

 with striae. This piece has much irregularity jn form and adjustment 

 with reference to the body, in different specimens, being disposed above 

 the general surface at its superior extremity, and sometimes below it; 

 frequently the circular notch occupies the whole summit of tha piece, 

 which is then, very prominent, and prolonged above the summit of the 

 body, while in other specimens it terminates a considerable distance 

 below the summit. 



The pseudambulacral fields, five in number, rise from the angular 

 notch in the summits of the second radials, and terminate at the sum- 

 mit; they are alike in size and arrangement of parts; each field- consists 

 of three parts, the middle of which is the longest; rising from the 

 bottom of the notch, as before stated, it is continued to the openings 

 around the summit, which it divides, and is continued beyond them 

 toward the center of the crown, and is lost under the small pieces ar- 

 ranged within the openings. It is divided by a line into equal parts 

 running its whole length, each of which is again divided into a line of 

 pores, and a ridge. In some states of specimens the mesial line is 

 deeply grooved, on either side of which is a rounded ridge, equal in 

 width to the line of pores; thus each field is divided into four parts of 

 equal width — i. e., two lines of pores and two ridges lying between 

 them. In large specimens their width is .^/ r of an inch. The pores 

 are ovoid, the long diameter lying transversely with the specimen, 

 about 60 to the inch; they terminate at the reniform larger openings 

 at the summit. The openings at the summit have their long diameter 

 parallel to the length of the pore pieces. 



The sides of the suture dividing the pore pieces is beautifully orna- 

 mented by fan-like figures, lying nearly opposite the pores; they are 

 nearly triangular in form, composed of six diverging ridges, having a 



