134 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



ACTINOCRINUS POCILLUM (n.s.). 



Body regularly hemispherical below the arms. Base with a com- 

 paratively large depression for the column-attachment, and a low 

 rounded tripartite rim formed by the thickening of the basal 

 plates. First radial plates of moderate size, wider than high. 

 Second radials much wider than high, hexagonal. Third radials 

 smaller than the second, broadly pentagonal or heptagonal; sup- 

 porting on each upper sloping face, in the anterior and postero- 

 lateral rays, a single supraradial plate, which gives origin to an 

 arm on each side, making four arms to each of these rays. In the 

 antero-lateral rays, those plates support an arm on each side, 

 giving only two arms. This makes a brachial formula, 



^ 4 . 



f-f =: 16 arms. 



TiRST interradial plate large, hexagonal; supporting two smaller 

 plates in the second range, with still smaller ones in the third, 

 uniting with the dome-plates. First anal plate smaller than the 

 first radials, heptagonal; supporting three smaller plates in the 

 second range, five in the third, and still more in the fourth, the 

 plates in each series smaller than in the preceding one. Arms 

 round, slender, with two bifurcations, composed of two series of 

 short plates interlocking on the back; the upper edges elevated, 

 producing a somewhat imbricate appearance, with granulosa 

 surface. 



Surface of plates marked by four small lozenge-shaped elevations, 

 covered by very fine radiating strise. These raised portions of the 

 surface occupy a triangular space on each side of tlie sutures 

 between adjacent plates, so that there are as many of these eleva- 

 tions surrounding each plate as there are sides to the plate : the 

 centres of the plates are also slightly elevated. 



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

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



ACTINOCRINUS : Subgenus MEGISTOCRINUS (Owen). 



MEGISTOCRINUS DEPRESSUS ( n: s.). 



Body rather large, broadly spreading, shallow. Dome depressed, with 

 strong deep constrictions or depressed areas between the rays and 

 their divisions, reaching to the centre, which is ornamented with 

 a strong spine : five other spines are at the junction of the ridge, 

 marking the divisions of each ray, about halfway from the centre 



