132 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



Geological formation and locality. In the shales of the Hamilton group: 

 Western New- York. C. A. White, collector. 



ACTINOCRINUS CAULICULUS ( n. s.). 



Body small. Calyx broadly cupshaped, approaching hemispherical, 

 with a thin projecting rim around the base; somewhat pentalobate 

 in a basal view, from the protrusion of the arm-bases and plates 

 of the radial series. Basal plates of moderate size, low, projecting 

 at the lateral margins. First radial plates proportionally large, 

 wider than high. Second radials small, pentagonal or hexagonal, 

 as wide as high. Third radials a little larger than the second, 

 pentagonal or heptagonal, supporting on each upper sloping edge 

 two supraradial plates of moderate size, one above the other : the 

 upper one of these is a bifurcating plate, and gives origin to two 

 arms, making four arms to each ray =i 20 arms. 



Interradial plates three in each series ; the first one hexagonal, 

 wider than high, supporting two smaller plates in the second 

 range : above this, they are more properly dome-plates. First 

 anal plate nearly equal in size to the first radial, heptagonal, 

 supporting three small plates in the second range, with a still 

 larger number in the third range. 



Arms becoming free above the third radial plate; composed in the 

 lower part of cuneate plates, and, above, of a double series of 

 interlocking plates, their length a little less than the breadth of 

 the arm, and their surfaces beautifully ornamented by granules 

 and small curving ridges. 



Surface of plates marked by a single set of low, rounded, radiating 

 ridges, which unite with those of the adjoining plates at the 

 sutures, and, meeting in the centres of the plates, they form 

 rounded or angular nodes. 



This species differs from either of the preceding in the structure and 

 number of the arms. In the arrangement of the calyx-plates, it is closely 

 related to A. nyssa ; but it is a smaller species, and differs in the number 

 of the arms. 



The four preceding species are remarkably similar to Carboniferous 

 forms of the genus ; and, aside from their well authenticated geological 

 associations, would in themselves offer no means of separation from the 

 Crinoidea of the Carboniferous fauna. 



Geological formation and locality. In shales of the Hamilton group : 

 Western New- York. C. A. White, collector. 



