384 PROCEEDINGS OP THE ACADEMY OF 



almost vertically to near the arms, where they curve a little outwards. Plates 

 nearly smooth or subgranulose, and all convex, chose of the subovate inter- 

 radial spaces less prominent than the rays, and showing a very slight tendency 

 to develope obscure ridges, one of which passes to each side; sutures mode- 

 rately distinct. Base small, entirely within the concavity of the underside, 

 concave, and obscurely pentagonal ; columnar facet large, or occupying 

 nearly the whole area of the base, obscurely marked by radiating stria?, and 

 provided with a small penatgonal star-shaped central opening. Subradial 

 pieces as wide as long, truncated, and narrower above than below, subquad- 

 rangular in outline , but provided with a fifth very obtuse angle in the middle 

 below, and having each inferior lateral angle slightly truncated. First radial 

 pieces larger than the subradials, and wedged so far in between them as to 

 come nearly in contact with the base, about as wide as long, heptagonal, the 

 sides connecting with subradials being longer than the others. Second radials 

 hexagonal, as long as wide. Third radials heptagonal, and supporting on their 

 superior sloping sides the first secondary radials, each of which is succeeded by 

 two others, the last of which supports the first true brachial piece. 



The first interradial pieces rest upon the superior truncated side of the sub- 

 radials, which are about equal in size ; they are all hexagonal, the inferior 

 lateral edges being very short, and the UDder side longer than either of the 

 others. Above these there are in the second range three, in the third three 

 or four, and in the fourth three pieces, the latter being surmounted by three 

 or four others ; all the series diminish gradually from below to the summit. 

 (Anal plates unknown.) 



The interbracbial pieces are all very small, two of them being wedged down 

 in the narrow space between the first and second secondary radial pieces, 

 while the others are arranged so as to form the upper and inner side of the 

 two small ambulacral apertures the outer and lower sides of which are 

 formed partly by a sinus in the edge of the second secondary radial pieces, 

 and parti}' by one side of the third. 



The secondary radials diverge so that those belonging to different rays meet, 

 over the centre of each interradial space, where the arms of which there 

 appear to be ten, arise. The first brachial pieces are not quite free, being 

 flanked on either side by the interbracbial pieces, forming the summit of the 

 apertures. They are all pierced directly through the middle by the arm 

 openings. 



The summit is very slightly convex, and composed of unequal plates, the 

 larger of which are tumid, and the smaller less convex. Extending from 

 each arm, towards the middle, there is a depression occupied by smaller 

 pieces, while the larger and more convex plates occupy the prominences be- 

 tween. The specimen examined being a little defective on one side, the exact 

 position of the anal opening, if any exists, cannot be determined. 



Height to top of first brachial pieces, 0-48 inch ; do. to ambulacral apertures. 

 39 inch ; do. to top of vault, 0-56. Breadth below the arms, 0-51 inch. 



Locality and position. Burlington Limestone of subcarboniferous series, 

 Burlington, Iowa. 



Genus ACTINOCRINUS, Miller. 

 Actinocrinus validus. Body of medium size, subglobose, being more de- 

 pressed above than below the arms ; calyx somewhat ventricose, and formed 

 of thick, convex, radiately costate plates, connected by moderately distinct 

 sutures ; summit composed of small irregular tuberculose pieces, and provided 



ambulacral openings may exist in the type of that genus, and that in consequence of the 

 ;mperfection of their specimens, Messrs Lyon and Casseday may have failed to see 

 them. If so, all the species will probably have to be ranged under their name, which 

 was first published, unless when the characters and limits of Acanthocrinus are better 

 known, it may be found that these American forms should only constitute a section of 

 that genus. Prof. Hal] seems to have overlooked the almost exact identity in the 

 generic formula of his group with that given of Goniaslcroidocrinus. 



[S 



cpt. 



