134 ECHINODERMS. 



forming a shallow, expanded cup ; projection of the columnar 

 facet broad and low. Radial plates narrow and very long, quite 

 two-thirds the entire length of the calyx ; bodies short and 

 obliquely bent inward, and subangular in the middle line ; limbs 

 with parallel margins, steep sides, and very obliquely truncated 

 above ; sinuses broadly lanceolate ; lips rather prominent ; in- 

 terradial sutures in concavities. Deltoid plates acutely and 

 unequally rhombic, and their surfaces concave ; radio-deltoid 

 sutures at about one-third the height of the calyx from the 

 summit. Ambulacra convex extending nearly the entire length 

 of the body, their proximal ends depressed below the edges of 

 the sinuses, but on a level with them distally ; lancet-plate 

 as wide as, if not wider than, the combined side plates on each 

 side ; ambulacral grooves wide and shallow, but the lateral 

 grooves slightly oblique ; side plates oblong, 40 to 50 in num- 

 ber. Three hydrospire-folds on each side ; spiricles oval, but 

 often in pairs, and separated by stony septa. Mouth small. 

 Ornament consists of fine lines parallel to the margins of the 

 plates. ( Eth. & C.) 



Horizon and locaUties.— ljOweT Carboniferous, Upper 

 Burlington limestone : Palmyra, Helton and Hannibal in Marion 

 county, Louisiana, Columbia, Eocheport (Boone county), Ash 

 Grove ( Greene county ), Ste. Genevieve. 



Pentremites conoideus Hall. 



Plate xviii, fig. 5. 



Peniremiies conoideus Hall, 1856: Trans. Albany Inst., vol. IV, p. 5. 

 Pentremites conoideus Hall, 1858: Geol. Iowa, vol. I, p. 655, pi. xxii, figg. 



8-10. 

 Pentremites conoideus Shumard, 1858: Trans. St. Louis Acad. Sci., vol. I, 



p. 243, pi. ix, fig. 4. 

 Pentremites conoideus Etheridge & Carpenter, 1886: Cat. Blastoidea, p. 162, 



pi. ii, tigs. 16-23 (in part). 



Like P. elongatus, but much smaller and conical. 

 Horizon and localities.— Lower Carboniferous, Keokuk 

 limestone : Boouville (Cooper county). 



