MUSEUM OF COMPARATIVE ZOOLOGY. 351 



into joints, except on the lower surface, which is smooth, and is uniformly 

 paved with small flat grains, looking, under the lens, like a rough mosaic. 

 Each of the raised joints is covered by a belt of four rows of grains run- 

 ning across the arm ; the two middle rows have smaller grains, each of 

 which bears a little saw, having four or five teeth, and at its end a strong 

 hook; the two outer rows have larger grains, without any appendages. 

 Each depression between the joints is paved with two or three cross-rows 

 of more or less flattened grains, similar to the smooth grains of the raised 

 joints. Towards the end of the arm the raised joints consist only of the 

 double row of grains bearing the saw-hooks. Disk, above, covered with a 

 mosaic of smooth, flat grains, from which rise a great number of short, 

 blunt, tapering, very stout spikes, the longest .8 mm. ; they are arranged 

 in about seven, more or less distinct, concentric circles, growing confused 

 at the centre of the disk, where there is a space about 3 mm. in diameter, 

 from the periphery of which spring the ten radiating ribs, which are very 

 narrow, though somewhat broader over the bases of the arms ; over these 

 ribs run the circles of spikes, giving them a rough, spinous appearance. 

 The interbrachial spaces below have a strikingly smooth appearance, though 

 really covered with minute, rounded, flattened grains of several sizes. 

 Between the bases of the arms, below, and connecting the first groups of 

 arm-spines, runs a little fence of three irregular rows of little, crowded 

 spikes, more blunt and rounded than those of the upper disk. Just outside 

 one of these fences lies the madreporic plate, which is small and elongated, 

 and has about a dozen large pores in an irregular row. The disk about 

 the mouth is quite flat and smooth, so that the animal, seen from below, is 

 laid out in regular patterns ; in the centre the stellate mouth rough with 

 spines ; outside this a five-sided smooth region, which is prolonged on each 

 arm; outside this a five-sided fence of spikes, which separates the mouth 

 region from the interbrachial spaces, and is prolonged by the bunches of 

 arm-spines along the side of the lower surface of each arm ; again outside 

 is the smooth interbrachial space, where the genital slits run from the edge 

 of the disk (marked by a margin of spikes) about two thirds of the way to 

 the interbrachial fence of spikes. Arm-spines equal, rounded, a little bent, 

 suddenly contracting at the end, where they bear a bunch of four or five 

 thorns ; they are arranged side by side, in close clumps, at the angle made 

 by the under surface and side of the arm; length of the longest, 1.2 mm. 

 The first tentacle pore has one little simple spine ; the second has four 

 thorny spines; the third, and several beyond, five; then the number is 

 four ; towards the end of the arm it diminishes to three, two, and one. 

 Near the tip, where there are but two, these spines have hooks at their 

 ends, and at the very end there is but one spine, which is like the saw-hook 

 borne by the grains on the back of the arm. Color in alcohol, yellow gray, 

 or straw color. 



