PEOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 201 



three to five, or more, polyp-cells, whicli are larger tlian in A. carneum, 

 and, wlien contracted, are obovate, incurved, and sliow the bases of the 

 eight tentacles as small terminal lobes. The spicnla are larger and 

 rougher than in A. carneum and the two preceding species. Height, 3 

 inches, or more. 



ECHINODERMATA. 

 Tremaster, gen. nov. 



Body thin, pentagonal, the rays united by a thin interradial web ex- 

 tending to their tips. Five interradial openings, situated toward the 

 center of the disk, pass directly through to the lower side, where they 

 open at the aboral side of the jaw-plates. Ambulacral grooves wide 

 toward the month. Suckers in four rows. Upper surface covered with 

 imbricated flat plates, which may bear granules and marginal spinules. 

 Lower surface with suiall imbedded plates, bearing spines. 



Tremaster mirabilis, sp. nov. 



Body thick in the central region, very thin at the margin, the ends of 

 the rays extending but little beyond the interradial margin, while the 

 interradial web extends in a rounded lobe a little beyond the proper 

 end of the rays, so that there is at the tip a shght but evident emargina- 

 tion. In all the specimens, the body is bent upward in a very convex form, 

 with the rays and margin bent abruptly downward, so that the edges 

 are in contact with the ground, or nearly so, all around, leaving a large 

 concavity underneath. The margin is thrown into a broad fold or un- 

 dulation between the rays. On the dorsal surface, the imbricated plates 

 of the radial regions are more prominent, thicker, and with a broader 

 fi^ee portion than those of the interradial regions, and they bear a row, 

 sometimes of eight to ten small, acute, appressed spines (often but one 

 or two in the young) along the free edge ; these plates form, therefore, 

 a regular rosette or star on the dorsal surface, its rays broad at the base 

 and rapidly narrowed toward the margin, where the plates become very 

 small and lack the spinules ; all the dorsal plates are covered with small 

 scattered granules, often with one or several larger central ones. In the 

 interradial areas, the plates are thin, flat, the inner or free ends are oval 

 and destitute of spines, and each plate is usually overlapped by only two, 

 laterally placed, and not by theone directly behind it, asinthe radial areas ; 

 these plates are large and somewhat rhomboidal toward the central area 

 of the disk, but become very small and rounded toward and at the margin ; 

 each minute lower marginal plate bears a small ovate spinule, which form 

 a close row or fringe around the margin. The central area of the disk is 

 covered by large granulated plates; four or five, somewhat irregular in 

 form, surround the central opening, which is protected by a circle of 

 about twelve to eighteen small, obtuse spines. Madreporic plate prom- 

 inent, close to the central opening, surrounded by small spinules. The 

 five disk-perforations are large and conspicuous, when distended ellip- 

 tical in form, and bordered by a row of small spines, which often con- 

 verge above it. The interradial areas of the lower surface are formed 



