NATURAL SCIENCES OF PHILADELPHIA. Ill 



entire breadth. Succeeding radials, of which there are three in each of the 

 rays seen* as wide as the first, but much shorter, or only one-third to one- 

 fourth as long as wide, thus forming free arms so wide' as to be nearly "in 

 contact all around, excepting on the anal side ; last or fourth radial support- 

 ing upon its superior slightly sloping sides, the first divisions of the arras, 

 which, at least in one of the posterior, and one of the lateral rays, bifurcate 

 on the third piece, while some of the divisions appear to divide again on the 

 f iurth piece, which is as far as they can be traced in the specimens examined. 

 Column large, or nearly two-thirds as wide as the base, at its connection with 

 the latter; but suddenly tapering downward, and, at least in one of the ex- 

 amples, ending with the sixth piece in a rounded point, evidently showing 

 this individual to have been free at maturity. Connecting, or upper joint, of 

 the column in the only two examples seen, very thick, and in one quite tumid. 



Height to summit of first radial pieces, 0-48 inch ; breadth of do., 0*50 inch : 

 height of base, 0-20 inch ; breadth of do., 0-24 inch; breadth of rays below 

 the first division, 0-17 inch. 



This species seems to be most nearly related to //. polydactylus of Shumard, 

 from which it differs in the remarkable narrowness of its base, and the pro- 

 portional greater thickness of its column. It also differs in having only three 

 to four primary radials to each ray, instead of five to six. 



Locality and position. Mount Carroll, Illinois. Cincinnati Group of Lower 

 Silurian. 



Genus CODONITES, M. and W. 



In the Proceedings for April of last year, page 84, we proposed, in a note, 

 to found a new genus under the above name, for the reception of Pentremitei 

 ftelliformis, of Owen aud Shumard. This genus agrees with Pentremites in 

 structure, excepting that its openings corresponding to those usually called 

 the ovarian apertures (Hydrospires, of Mr. Billings), instead of forming with 

 the larger opening, usually called the anus, five round apertures, appear 

 at the surface as ten elongated slits, widest at the upper and inner ends, and 

 situated one on each side of each of the so-called pseudo-ambulacra. f Again 

 its aperture, corresponding to that usually considered the anus in Pen'remites, 

 is proportionally larger, more remote from the center of radiation, and com- 

 pletely disconnected from the so-called ovarian opening on each side of it. 

 As in Pentremites, the central hiatus is covered by small plates in perfect speci- 

 mens, and from this little disc of plates two rows of minute alternating pieces 

 are seen to extend out, so as to cover each of the little ambulacral furrows, 

 passing along the middle of each pseudo-ambulacral area and under the cen- 

 tral disc, into the covered central aperture. These little covering plates of 

 the furrows probably extended the whole length of the pseudo-ambulacra, 

 but were doubtless movable, or capable of opening along the middle, being in 

 fact marginal ambulacral pieces. 



As in the genus Pentremites, we also observe in this type three pieces an- 

 chylosed to the bottom of the busasal pieces, with the sutures between them 

 exactlv coinciding with those separating the three busas pieces ; these we pro- 

 pose to call supplementary basal pieces.* The internal folds, or compressed 



The right posterior ray seems to be an exception to this statement, as it appear, to 

 have only three radials including the first, with the second one nearly as large as the 



^Wrtja^t^ *"" to th0Se f 



wmmsssmmmm 



done bv Mr. Billings, in an interesting paper on the stiucture oi , '' e T 1 ;,' ' s ';o The 



