466 PALEONTOLOGY OF ILLINOIS. 



mentary .pore pieces, if any exist, unknown. So-called 

 ovarian openings, commencing one on each side near the 

 inner ends of the pseudo-ambulacral, or arm areas, and 

 e ^tending ontward along the margin of a broad snlcns, and 

 near the edges of these areas, for about half the length of the 

 latter, as very narrow slits, widest at the inner end, where 

 they connect with the inner ends of the internal compressed 

 tubes under the areas,* Central hiatus very small, its cov- 

 ering pieces minute; ambulacra! canals passing in under 

 the little central disc into the central hiatus, each covered 

 apparently all their length, in perfect specimens, by a 

 double series of very minute, interlocking pieces, doubt- 

 less capable of being opened apart along the middle during 

 the life of the animal. Surface in well preserved specimens 

 ornamented with regular, moderately distinct strisB running 

 parallel to the margins of the basal and radial pieces. Col- 

 umn below the upper anchylosed part forming the supple- 

 mentary base, and pinnulae unknown. 



Hight of a medium size specimen, exclusive of the sup- 

 plementary base, 0.80 inch; greatest breadth, 1.34 inches; 

 hight of supplementary base, 0.17 inch; breadth of do., 

 0.30 inch; breadth of pseudo-ambulacra, or recumbent arms, 

 about 0.08 inch. 



In general form this species seems to be remarkably like Pentremites 

 inflatus, Gilb., as figured by PHILLIPS in his Geol. Yorkshire, pi. 3, fig. 

 1 5 but as PHILLIPS' figure does not show the summit, and gives but a 

 few words of description, we have no means of knowing whether or 

 not it belongs even to -the same genus. 



Locality and position Lower bed of the Burlington group, of the 

 Lower Carboniferous series, at Burlington, Iowa. Some of the best 

 specimens of this species we have seen belong to Mr. WACHSMUTH'S 

 collection. 



* These slits seem, as it were, to cut off a thin slice from each of the edges of the anal and inter- 

 radial pieces, a* well as from the margins of the deep pseudo-ambulacral sinuses of the radials. 

 These slices are thicker near the upper (inner) ends, where they sometimes become callus, and 

 apparently anchylosed, in adult specimens, to the pores pieces, so as to give the pseudo-ambulacra 

 the appearance of greater breadth there thau is natural. 



