NATURAL SCIENCES OF PHILADELPHIA. 149 



stricted around the middle ; pentagonal in form, the upper angle being rather 

 salient, and each supporting an arm on each of their superior sloping sides. 

 First anal piece about one-third as large as one of the subradials, hexagonal 

 in form, and resting between the upper sloping sides of two of the subradials, 

 and partly under one side of one of the first radials on the right ; while it sup- 

 ports another anal piece above, and connects with a third on the left, which 

 rests upon the upper truncated side of one of the subradials. 



Arms moderatelj'long, carinated along the middle of the outer side, and 

 after the first division on the second radials dividing again on the sixth or 

 eighth piece, beyond which they are all simple ; each composed of alternating 

 wedge-shaped pieces, which are a little wider than long, and each projecting 

 on alternate sides above for the reception of tentacles, which are stout, angu- 

 lar, and composed of pieces nearly twice as long as wide. 



Breadth of body, 0-55 inch ; height to top of first radials, about 0-20 inch. 



This species is remarkable for the curious rough appearance of the arms, 

 produced by the projection of the pieces alternately on each side, and the in- 

 terruption of the carina along the dorsal side, which is not continuous, but looks 

 as if the pieces had been slipped a little alternately to opposite sides. 



Locality and position. — Crawfordsville, Indiana. Keokuk division of the 

 Lower Carboniferous. 



Subgenus ZEACRIXUS. 



Zeacrinus scobina, M. and W. 



Body very much depressed, or about four times as wide as high, to the top 

 of the first radial pieces, and concave in the middle below. Base small, and 

 hidden by the column in the concavity of the under side. Subradial pieces 

 curving in to the concavity of the under side, and extending outward 

 around the column ; all presenting a nearly pentagonal general outline, 

 with short lateral edges, excepting the one on the anal side, which seems to 

 be hexagonal, (each being without a visible angle at the middle of the under 

 side). First radials three or four times as large as the subradials, near twice 

 as wide as long, pentagonal in form, with lateral and inferior margins of nearly 

 equal length, and upper edge equaling the entire breadth. Second radials 

 as wide as the first and nearly twice as long, all pentagonal in form, the supe- 

 rior angle being salient, and also projecting outward, while a strongly defined 

 mesial angle extends down the middle of the dorsal or outer side to the base 

 of each, the surface on each side of this angle being distinctly concave. 



Anal pieces small, and owing to the rough surface of the plates, and the in- 

 distinctness of the sutures, without very clearly defined outlines. As near as can 

 be made out, the first one seems to be somewhat cuneiform, and wedged in 

 obliquely under one side of the first radial on the right ; on its left it connects 

 above the middle, apparently with another resting upon a very short upper 

 side of one of the subradials. Above these other anal pieces are seen between 

 the arms, but their exact arrangement cannot be made out from the specimen 

 studied. 



Arms, after their origin on the second radials, each bifurcating on the sixth 

 piece (excepting those of the anterior ray, which divide first on the eleventh 

 piece), the inner division of each being smaller than the other, and remaining 

 simple ; while the outer or main arm gives off another division on the inner 

 side on the eighth piece above the first bifurcation, and still another on the 

 ninth or tenth piece above the latter, which is as far as the arms can be 

 clearly traced in the specimen, though there is some appearance of a fourth 

 bifurcation in one of the arms. Arm pieces short, or from twice to three 

 times as wide as long, and not in the slightest degree wedge-shaped ; each with 

 lateral edges sharp and a little projecting, and provided with a little pointed 

 process on the middle of the dorsal side. These little asperities, and the bev- 

 eled character of the sutures between the arm joints, give the arms a rough, 



1869.] 



