ECHINODERMATA—BLASTOIDEA. 48 1 



VI. Pentremites Say. 

 Calyx usually ovate or pear-shaped, with elongate, subtruncate, 

 never trilobate base; summit sometimes flat, seldom convex. 

 Basals small, forming a small cup. Radials long, forming the 

 greater portion of the calyx. Deltoids small, sometimes concave. 

 Ambulacra broad, subpetaloid. Lancet plates wholly exposed and 

 resting below on '' under lancet plates." Side plates and outer 

 side plates numerous, the former abutting against the edges of the 

 lancet plate. Hydrospires three to nine. Spiracles single or occa- 

 sionally double, the two of the posterior side confluent with the 

 anus and forming with it a single large opening. Summit covered 

 with numerous spines (usually broken off in the fossil) placed 

 closely against one another so as to form a pyramid which com- 

 pletely covers the summit of the greater portion of the spiracles. 

 Mississippic. 



A. Large (breadth usually i inch or more) I. 



I. Height of calyx exceeding breadth 14, F. obesus. 



1. Height and breadth about equal a. 



a. Base very short 16. P. sulcatus. 



a. Base long 17. P. cervinus, 



B. Small (breadth usually less than i inch) 2. 



2. Height of calyx exceeding breadth b. 



b. Calyx elliptical 9. P. elongatus. 



b. Calyx ovoid, i. e., greatest diameter usually belovir middle.. 10. P. conoideus. 



b. Calyx pear-shaped, greatest diameter about the middle , *. 



*. Outline long, oval 15. P. pyriformis. 



^. Outline broad, oval II. P. elegans. 



2. Height and breadth about equal c. 



c. Calyx globular, i. e., greatest diameter near middle 12. P. globosus, 



c. Calyx ovoid, i. <f., greatest diameter below middle 13. P. godoni. 



9. P. elongatus Shumard. (Fig. 1792, a, b.) Mississippic. 



Length of calyx nearly or quite twice the breadth. 

 Burlington of Iowa and Missouri. 



Fig. 1792. a, b, Pentremites elongatus^ a robust and a slender individual ; cy 

 Granotocrinus norwoodi, outline of a rotund form; d^ Pentremites conoideus. (After 

 Etheridge and Carpenter. ) 



