MUSEUM OF COMPAKATIVE ZOOLOGY. 143 



large part of their length, long, narrow, joined, raised above surrounding surface ; 

 scaling hidden. Five or six essentially smooth, tapering, and nearly equal arm- 

 spines, of which, however, the upper one is much the stoutest ; lengths to that 

 of an arm-joint 1.8, 1.6, 1.5, 1.5, 1.5 : 1.2, or 2.2, 1.6, 1.5, 1.3, 1.3, 1.3 : 1.2. 

 Tentacle-scales flat, pointed, and rather small. Color in alcohol, pale brown. 



The species stands near the typical 0. setosa in respect to form of di.sk and 

 length of arm ; but it differs from this and mo.st others of the genus in having 

 naked radial shields and side arm-plates, which do not project to give a knotted 

 look to the arm. 



Station 33, off Bermudas, 300 fathoms, 1 specimen. Two specimens from 

 the "Blake" expedition, dredged in 101 fathoms by A. Agassiz, showed no 

 important variations. The disk-grains were larger and more numerous. 



Ophiacantha cuspidata sp. nov. 



Plate X. Figs. S48 - 250. 



Special Marks. — Disk beset with thorny stumps ; eight rather long, stout, 

 and feebly thorny arm-spines : about eleven long slender mouth-papilUe. 



Description of an lyuUvidual (Station 344). — Diameter of disk 9 mm. Length 

 of arm 63 mm. Width of arm without spines 3 mm. Ten or sometimes eleven 

 long, flat, rather slender and irregular mouth- papillae, of which the outer one 

 has often a spatula shape. Teeth long, spearhead-shaped. Mouth-shields 

 small, long pentagonal, with a wide obtuse angle within ; length to breadth 1:1. 

 Side mouth-shields small, narrow, and crowded, meeting within. Under arm- 

 plates wider without than within, where they touch the next plate ; bounded 

 without by a roimded angle or a somewhat deep curve, within by a more gentle 

 curve, and on the lateral sides, opposite tentacle-scales, by re-entering curves. 

 The second plate is narrower within, and has a wavy outer edge. Upper arm- 

 plates fan-shaped, with an angle iuAvards ; the lateral corners are sharp, and 

 the lateral sides slightly re-enteringly curved. Side arm-plates moderately 

 prominent, meeting narrowly above, but not below at base of arm. Disk 

 moderately thick, not puffed, closely set with stout little stumps each bearing 

 a crown of five or six minute thorns. Radial shields and disk-scales hidden 

 by skin and tlie thorny stumps, except that the position of each radial shield 

 is usually marked by a shallow furrow. Eight stout, long cylindrical arm- 

 spines, tapering to a blunt point and set with fine thorns ; lengths to that of an 

 arm-joint 3.6, 5, 3, 2, 2, 2, 1.8, 1.4 : 1. On first pore two tentacle-scales ; on 

 the rest a single large pointed scale. Color in alcohol, dark straw. 



A young specimen with a disk of only 1.5 mm. had an arm of 10 mm. The 

 disk armature was little crochets with two or three prongs ; the arm-joints 

 were of course more constricted, and the upper and under arm-plates were 

 widely separated ; there were four or five arm-spines^ whereof the first or 

 second was much the longest ; to each mouth-angle seven papilla), whereof the 

 lateral were bead-like and had not yet become long and slender. 



Station 344, 430 fatlioms, 12 -|- and 5 young specimens. 



