FOSSILS OF THE NIAGARA GROUP. 127 



between the arm bases. The anal area is much larger than the inter- 

 radial areas, and consists of a first plate, nearly equaling in size that of 

 the first radials, and supports three in the second arid five in the third 

 range, above which point they are not so regularly disposed, but the cen- 

 tral plates of the area form a direct line with the first anal plate, and 

 along the middle of the proboscis, for some distance above its base. The 

 proboscis is very long and slender, composed of elongate polygonal plates, 

 of which there are four or five in a series near the base, but often not 

 more than three in the upper part. The proboscis preserved in the 

 specimen described is nearly an inch and three-eighths long, and still 

 imperfect at the upper extremity, where it is less than an eighth of an 

 inch in diameter. 



The general surface of the plates of the body is highly convex, with 

 deeply channeled sutures, the smaller ones, near the upper portion of the 

 cup, and on the dome, being very convex. The surface of each plate is 

 also ornamented by a system of radiating lines, those meeting at the 

 center of the plate extending to the angles. On some of the plates there 

 is an appearance of intermediate lines, the number of which can not be 

 determined. 



The species is described from an internal cast and a gutta-percha im- 

 pression of the exterior obtained from the matrix of the same individual, 

 which gives the form and surface o5 the plates. The arm bases, includ- 

 ing the intersupraradial areas, are elevated, and project beyond the gen- 

 eral level of the body, giving a somewhat pentalobate feature to this part 

 of the body. The impression of a fragment of the column is preserved, 

 and shows that this appendage was of medium size, and composed of 

 alternating larger and smaller plates. 



The species most nearly resembles 5. speciosa, ,Hall, from the Niagara 

 shales of New York, but differs very materially in the external features 

 of the plates composing the body. In that species the plates of the body 

 are flat, or have only the general convexity of the cup, and marked with 

 indistinct radii, while along the radial series a low, rounded, rather in- 

 distinct ridge passes to the bases of the arms, and the arm bases do not 

 protrude beyond the general surface until they reach the top of the sec- 

 ond supraradial plate, while in this species the protrusion commences 

 with the third radial plate itself. From S. Christyi, Hall, it differs in 

 having only two arms to the ray at the top of the cup, instead of four, 

 as in that one. It also differs in this respect from S. Tennesseensis, Troost. 



Formation and locality: In limestones of the Niagara group, at Yellow Springs, 

 Ohio. Ohio State Cabinet. Collected by Prof. Edward Orton. 



