ARiEOSOMA LEPTALEUM. 185 



are separated only near the corona by the small irregular wedge-shaped 

 interambulacral plates. Such an arrangement is suggestive of Bothrio- 

 cidaris, where the interambulacral area is reduced to a minimum. 



The abactinal system is comparatively small (PI. 77, fig. 2). The 

 genital plates are pointed triangular with rounded angles, while the genital 

 membranes are elongated and more or less rectangular. The genital plate is 

 made up of two parts, a small outer piece distal to the membrane and a 

 broadly horse-shoe-shaped plate proximally, which carries from one to three 

 small secondaries or miliaries. The madreporic body is transverse elongate 

 with slightly concave sides. The anal system is covered with two outer 

 rows of larger polygonal plates, each carrying one or two secondaries or 

 miliaries and two or three interior series of small elliptical and polygonal 

 plates adjacent to the anus. 



The pedicellariae of this species are remarkably indistinctive, and it has 

 not seemed necessary to figure them. No dactylous pedicellariae were found. 

 The tridentate pedicellariae are not very abundant and show comparatively 

 little diversity of size. Most of them have the heads about a millimeter 

 long and the stalk three or four times that length. The shape of the head 

 and valves is much like what we find in thetidis (see PI. 66, fig. 17), but 

 some pedicellariae are much more like those of Sperosoma (see PL 64, 

 fig. 9). Occasionally one is met with which approaches fig. 12, PI. 67, and 

 the valves are often broadened distally and narrowed near the base, like 

 fig. 13, PI. 67. 



The triphyllous pedicellariae are more common, though hardly abundant. 

 The necks and stalks are very long and slender ; the valves are very much 

 like that shown in fig. 19, PI. 66, but are not quite so flattened or abruptly 

 widened at the tip. 



The sphceridia are very long and club-shaped, reminding one very much 

 of those of the previous species (eurypatiim). 



The single specimen of this interesting species was taken by the 

 " Albatross " at the following station : 



Station 4621. Off Mariato Point, Panama; 6°36'N., 81°44'W. 581 

 fathoms ; modern green-sand ; temperature of bottom not recorded, but 

 adjoining this station, 40.2° was recorded in 555 fathoms, in 1891. 



