464 PALEONTOLOGY OF ILLINOIS. 



basal pieces, and almost appearing as parts of the latter.* These do 

 not alternate with the basal pieces, but have the sutures between them 

 exactly coinciding with those of the base. These pieces might, for con- 

 venience, be called supplementary basal pieces, and will, in their dif- 

 ferent modifications, often furnish good specific characters in this genus, 

 as well as in Pentremites, and hence ought to receive especial attention 

 in specific descriptions. 



OODONITES STELLIFORMIS, M. and W. 



PI. 9, fig. 5. 



Pentremites stelliformis, OWEN and SHUMARU, 1850. Jour. Acad. Jfat. Sci., Phila., Vol. II, p. 67. pi. 



7, tig, 16 ; also (1852) in OWEX'S Geol. Report, Iowa, Wiscon. and Minn., p. 593, tab. V a, fig. 10. 

 Cadaster stelliformis, SHUMAKU, 1865. Cat. Pal. Foss., Part I, Eohinoid. p. 359. 



BODY pentagonal-obpyrifonn, being very narrow below, 

 and rapidly expanding upward from the base to the outer 

 (lower) extremities of theso-ealledpseudo-ambulacral areas, 

 and depressed convex above, where it presents a distinctly 

 pentagonal outline, owing to the deep interradial and anal 

 sinuses. Supplementary basal pieces forming a short, 

 rounded, stem -like projection, apparently distinctly thicker 



* Mr. S. S. LYOX was the first author, so far as we are aware, who called attention to these pieces in 

 Pentremites, and showed that they are really separable from the basal pieces, in sonit- cases, (See 

 Owen's Kentucky Geol. Report, Vol. Ill, p. 468). He, however, regarded these lower pieces as the 

 true basal pieces, and those above, usually considered the basals, as really being true subradial pieces. 

 At one time we were inclined to adopt this conclusion, as has recently been done by Mr. BII.LIXGS, in 

 an interesting paper on the structure of the lilastoidea, etc., published in the American Journal of 

 Science and Arts for July, 18C9. The fact, however, that these lower pieces do not alternate with the 

 range above, that Mr. LYON'S view would require should be considered subradials, as in the Crinoids, 

 provided with both basal and subradial pieces, would alone he an objection to this conclusion. It is 

 also worthy of note that when these lower pieces are removed, we find the next range of pieces above 

 closed together, so as to form the bottom of the visceral cavity. Again, in those species of Granato- 

 crinus, like (}. Norwuudi, with a deep concavity in the under side, we find the pieces corresponding to 

 those Mr. LYOX thinks are the subradials, as it we're, pushed inward, and forming a little pyramid 

 ill the bottom of the visceral cavity, precisely as we see the true basal pieces in various types of true 

 Criuoids, with a deeply sunken base. In addition to this, although adult specimens of the type of the 

 genus under consideration, have these lower pieces as solid as we see them in the true Peutremiti'!t, 

 young individuals show clearly that they arc actually composed of five or six of the npp<>r juintn of the 

 column, enlarged and am-lii/l/K/'il together. The swelling out or enlargement of some of the upper 

 joints of the column of a Criuoid, is no very uncommon occurrence for instance, in such genera as 

 Forbeniocrinuii. Poterioeriniten, Apiocrinites, etc. It is true that in these and other similar cases, the 

 enlarged upper joints of the column are not divided by vertical sutures, as in Pentremites and Codon- 

 ites. This fact, however, -will be seen to be of little importance, when it is remembered that the lon- 

 gitiulinal division of the column by vertical sutures still does occur in some true Crinoids as, for 

 instance, in Itfin/ci rnim. in which the, whole column is sometimes seen to he divided all the way down 

 into five sections. And it is a significant fact that these five sutures in the column of Harycrnnus 

 exactly coincide with those separating its five liasai pieces, exactly as the three sutures dividing the 

 pieces into three basals coincide with those separating the three basal pieces in I'rnti-i>m!ti>x and Co- 



lltlll it''X. 



