344 REPORT ON THE STATE CABINET. 



not more than one thousand feet above the upper beds of the Hamilton 

 group. Up to the present time the species is not known in any other 

 locality, and it remains the earliest known form of this group of fossils. 



GENUS AGELACRINUS, Vanuxem. 

 Agelacrinus hamiltonensis. 



Agelacrinus hamiltonensis, Vanuxem. Rep. of Third Geol. Dist. N. Y., pp. 158, 306, fig. 80. 



Body comparatively large, discoid or depressed-convex; the border com- 

 posed of several ranges of imbricating plates, those of the marginal 

 range minute, the others gradually increasing in size towards the 

 inner edge of the border. The range of plates adjacent to the inner 

 area or disc is composed of large transversely elongate plates, with 

 alternating smaller ones. Arms long, slender, curving ; the anterior 

 arm and the left antero-lateral and postero-lateral arms sinistral, the 

 other two dextral. The extremity of the right postero-lateral ray 

 extends into the anal area, and passes just behind the ovarian pyramid. 

 The arm-grooves are covered by a large number of elongate triangular 

 plates, arranged along their margins ; those of the opposite sides 

 alternating, and their adjacent ends interlocking. The arms have 

 their origin in a transverse pyramid, situated in the central area 

 about two-fifths of its diameter from the anterior margin: this 

 pyramid is composed of six plates, five of them triangular, their 

 bases forming the termination of the rays, and their apices uniting 

 above ; the sixth or posterior plate, rising from the anal area, 

 is larger and somewhat shield-shaped. The ovarian pyramid is 

 scarcely elevated, situated subcentrally in the largest interradial 

 area, composed of nine very elongate triangular plates. Interradial 

 areas composed of comparatively large polygonal plates (not squa- 

 mosely arranged or imbricating), uniting by their lateral faces, and 

 their centres elevated into angular ridges. The surfaces of the 

 squamose plates which form the border, are simply granulosa. 



This species, the type of the genus, difiers from all others yet described, 

 in having two of the rays dextral and three sinistral ; also the plates 

 composing the interradial areas are not squamose, as in most other species. 

 The pyramid, originating the arms, is composed of a greater number of 

 plates than any of the Silurian species of the genus. 



