470 PALEONTOLOGY OF ILLINOIS. 



an entire spine, wanting only an inch or two of the inferior extremity, 

 exhibits the connection of the singular swollen apex, with its claw- 

 shaped tuberculose processes, to the body of the spine, a relationship 

 which would hardly be suspected were the two parts found detached, 

 as they generally are. The large spinose hooks of the extremity in this 

 specimen seem to be traversed by a cavity connecting with the internal 

 or pulp-cavity, and tilled with a soft chalky substance. Other speci- 

 mens, however, exhibit, on removing the smooth external shell, au inner 

 dense core, but with an exceedingly delicate perforation, which is appa- 

 rently in direct communication with the coarse medullary canals which 

 traverse the body walls. 



Position and locality : Not common, fish-bed horizon in the upper 

 part of the Keokuk limestone, Lagrange and St. Francisville, Missouri ; 

 Keokuk, Iowa; and possibly in the fish-bed of the lower or division 

 beds at Nauvoo, Illinois. 



Batacanthtjs stellatus. 



PI. XXI, Fig. 1, 2, 3. 

 Drcpanacanthus ? stellatus, Newberkt and Woetuex, 1866, Geol. Snr.UL, Vol. H, p. 125, PI. XH, fig. 7. 



Spines of medium size, gradually tapering to an obtuse point, mode- 

 rately curved, transverse section subovate, lateral surfaces compressed 

 and regularly rounded into either border. Lateral face marked by 

 twelve to sixteen, more or less, obscure, closely approximated, longitu- 

 dinal costse, ornamented in the middle region by delicate, subcorneal, 

 strongly sculptured tubercles, separated vertically by twice or three 

 times their diameter, and arranged in irregular diagonal order, the 

 series generally extending obliquely upwards from the anterior border. 

 Towards the upper part in the convex posterior side the tubercles 

 become suddenly enlarged to several times their dimension in the late- 

 ral faces, widely spaced vertically, laterally compressed or vertically 

 elongated, strongly ridged, with their obtuse, eccentric apices below the 

 middle, and forming about five rows embracing the rounded margin ; 

 in the lower portion of the spine the tubercles of the posterior border 

 present scarcely appreciable difference in size and form from those in 

 the lateral faces. Along the anterior border, and perhaps extending 

 nearly to the base and probably reaching to the apex, several more or 

 less regular rows, at least four iu some examples, of strong, more or less 

 laterally compressed, trenchant, recurved denticles occur, those on 

 either side of the median line being largest, and apparently irregularly 

 interspersed with small tubercles similar to those in the lateral surfaces; 

 the large denticles are sometimes scattered at irregular intervals in the 

 body of the spine, especially in the upper portion, and in most instances 



