554 TRANS. ST. LOUIS ACAD. SCIENCE. 



more stem-like appearance. Fork-pieces elongated ; their base 

 portion occupies two-thirds of the entire length and slopes from 

 the apex of the ambulacrum gently downwards, but more abruptly 

 to both sides, giving thus a depressed appearance to the interam- 

 bulacral space. Deltoid pieces short. Ambulacral fields narrow 

 lancet-shaped, with the greatest transverse diameter near the 

 junction of the deltoid and fork-pieces. Lancet pieces nearly as 

 wide as the sinus, and sloping from the median line to the mar- 

 gin of the ambulacrum, thus forming on both sides of the mar- 

 gin a kind of triangular groove which is filled out by the poral 

 pieces. Poral pieces small, numbering nine to one-tenth of an 

 inch. All openings on the summit like those of Codonites stelli- 

 formis^ i.e. one longitudinal slit to both sides of the ambulacral 

 field for the ovo-spiracle openings and a large round one later- 

 ally. Surface apparently smooth and not ornamented. 



Dimensions — Greatest diameter at the apex of the ambulacral 

 field, five-sixths of the entire length of the calyx ; vertical height 

 from articulation surface of column to apex of ambulacral field, 

 two-thirds of the entire height. 



Geological formation and locality — In the lower Burlington lime- 

 stone at Sedalia, Mo. The specimen is in the collection of Mr. 

 • F. A. Sampson, of Sedalia. 



For better comparison and to show the difference between it 

 and Codonites stelliformis^ I have also given the figure of a me- 

 dium size specimen of the stelliformis (pi. D, fig. lo) from Bur- 

 lington, Iowa. 



EXPLANATION OF PLATE C. 

 Melonites crassus. 

 Melonites irregularis. 



Oligoporus parvus. 



EXPLANATION OF PLATE D. 



ArchcEocidaris Netuberryi. 

 Penlremites Sampsoni, natural size. 



The same enlarged. 

 Pentremites Raemeri, Shumard, natural size. 

 The same en arged. From the original of the Shumard collection now in Wash- 

 ington University. 

 Fig. 4. Pentremites granulosus. Meek and Worthen, natural size. 



4a. The same enlarged. From the original in the collection of Prof A. H. Worthen. 

 Fig. 5. Penlremites gemmiformis. 

 Figs. 6 & 7. Pentremites calycinus, Lyons. 

 Figs. 8 & 9. Codonites campanulatus. 

 Fig, 10. Codonites stelliformis , Owen and Shumard. 



