PLATE I. 



Pentremites pyriformis, Say, p. 167. 



Page 



Fig. 1. Portion of an ambulacrum, exhibiting the median food-groove with its more or less 

 transverse lateral branches, side and outer side plates, pores, and the grooves 

 proceeding from them on to the surfaces of the side plates. Subcarboniferous, 

 Kentucky. x 10 60 



Fig. 2. Portions of the ambulacrum of another example taken at three different heights, 

 showing similar characters, with slight modifications. Subcarboniferous, 

 Illinois. Coll. Wachsmuth. x 10 60 



Fig. 3. Portion of another ambulacrum, seen rather obliquely from above. Subcarboni- 

 ferous, Alabama. x 10 60 



Pentremites elongatus, Shumard, p. 161. 

 Fig. 4. View of summit, the spiracles single. Subcarboniferous, Iowa. Coll. Wachsmuth. 



x4 101 



Fig. 5. View of summit, the spiracles rendered double by the prolongation inwards of the 



central ends of the deltoids. Subcarboniferous, Iowa. x 4 101 



Pentremites pyriformis, Say, p. 167. 



Fig. 6. View of a portion of the summit. Two of the ambulacra have the lancet, side, and 

 outer side plates removed, so as to expose the under lancet-plate, the tops of the 

 hydrospires, and the ambulacral openings. Subcarboniferous, Illinois. Coll. 

 Wachsmuth. x4 43 



Fig. 7. A single radial sinus of the same specimen. x 4 48 



Pentremites sulcatus, Roemer, p. 165. 

 Fig. 8. View of summit, exhibiting the central dome of somewhat irregular plates partially 



broken through, and its extension outwards into the covering plates of the 



ambulacral grooves. Subcarbouiferous, Illinois. Coll. Wachsmuth. x 4 . .65 



Fig. 9. Portion of an ambulacrum, with the ambulacral groove exposed, and the nearly 



horizontal lateral grooves. Subcarboniferous, Illinois. x 6 61 



Fig. 10. Three of the spiracles, from the same specimen as fig. 0, with the central ends of 



the deltoids marked by tubercles. x 3 101 



Pentremites Godoni, Dcfrance, sp., p. 157. 

 Pig. 1 1. Portion of summit, with three of the spiracles divided by the septa, or central ends 



of the deltoids. Subcarboniferous, Iowa. x3 103 



