10 LYMAN ON A NEW STRUCTURAL 



than long, with a rounded, truncated angle within ; slight reentering curves on the lateral 

 sides, and the outer edge curved. Side arm-plates, short and thick, with cleanly curved 

 outer margin ; separated above by the large upper arm-plates which are much broader 

 than long, and strongly arched, with outer side straight, except at the corners where it is 

 rounded; length to breadth 4.-5 : 1.3. Disk thick but flat, with a notch over the arms; 

 it is covered, including radial shields and space next mouth-papillae, with an even, fine gran- 

 ulation; thirteen grains in 1 m.m. long. Genital openings long, extending from outer 

 edge of mouth-shield nearly to margin of disk. Ten short, flat arm-spines with rounded 

 ends, about two-thirds as long as a side arm-plate, except the lowest which is longer and 

 larger. Two small, round tentacle-scales, whereof one covers the base of the lowest arm- 

 spine. 



Color in alcohol nearly white. 



" Challenger," Station 219, N. E. of New Guinea; 152 fothoms ; 1 specimen. 



This species agrees in the number of disk-grains with 0. Yo'ldii, but has twice as many 

 arm-spines. O. fallax and 0. aster agree with each other as to grains, (about twenty-five 

 in the length of 1 m.m.), O. aster, however, has six arm-spines, instead of eight, and the 

 entire mouth-angle, including mouth-shield, is closely granulated. Finally O. Petersi has 

 about eighteen grains in the length of 1 m.m., six arm-spines, and naked radial shields. 



Ophiactis pectorale, s2d. nov. Plate II, figs. 26-28. 



Special marks. Disk without spines, and covered with thick, rounded scales, whereof 

 the largest are near the radial shields. Two small tentacle-scales. 



Description of an individual. Diameter of disk, 7 m.m. Length of arm about 

 38 m.m. Width of same, close to disk, without spines, 2 m.m. Three large, flat, irreg- 

 ular mouth-papillae on either side of the mouth angle ; and one long, thick, blunt papilla, 

 or tooth, at the apex. Mouth-shields slightly swollen, wide diamond-shaped, with rounded 

 angles and a slight lobe without; length to breadth, 1:1. Side mouth-shields short, wide 

 and of nearly equal width, meeting fully within. First imder arm-plate small, longer 

 than wide, five-sided with rounded angles and curved outer edge ; beyond, the plates are 

 much broader than long, with an ill-marked angle within, short deep reentering curves on 

 the lateral sides, and outer side long and cleanly curved. Side arm-plates short ; nar- 

 rowly separated above and beloAV. Upper arm-plates much wider than long, thick, 

 slightly arched, with a broad rounded angle within, acute angles on the lateral sides, and 

 outer edge gently curved. Disk thick, having deep radiating constrictions in the inter- 

 brachial spaces, extending even to the centre : — it is covered with large, thick, flat, 

 rounded, overlapping scales; those in the centre being much finer than those without, 

 and the largest are arranged in rows radiating from the radial shields. These are large 

 and stout, about as broad as long, and of an irregular triangular shape, with the outer 

 end rounded; length to breadth 1.4 : 1.1 ; they are separated by a row of two or three 

 large, rounded over-lapping scales. On the under surface the scaling is much finer than 

 above. Four or five short, blunt, cylindrical, slightly tapering arm-spines; upper one 

 longest and somewhat longer than an arm-joint. Two tentacle-scales, one small and lip- 

 like, on the under arm-plate ; the other oval and on the side arm-plate. 



Color in alcohol, — straw. 



