SHALLOW-WATER STARFISHES 275 



that they stand free within the cavity, thus leaving the membrane 

 unsupported along the slits. On the ventral side the rays are nearly 

 flat, and the disk around the mouth is deeply concave. 



" Each ray is broadest at the margin of the disk. The transverse 

 adambulacral combs are numerous and covered with a thick, firm 

 skin, which entirely conceals the spines in alcoholic specimens. On 

 the broadest part of the ray, opposite the margin of the disk, there 

 are mostly four, rarely five, spines of moderate length in each comb ; 

 of these the one next the groove is somewhat shorter than the two or 

 three which succeed it, while the outermost is still shorter and 

 directed more outward, so that the group has a somewhat rounded, 

 but not very elevated, scolloped margin, the membrane receding 

 somewhat between the points of the spines. The spines, when 

 exposed, are rather slender, flattened, rough, and truncate at the flat 

 tip; beyond the outer spine the web rapidly becomes less elevated 

 and each comb lies somewhat obliquely over the one next beyond it, 

 and becomes only a slightly elevated broad fold before reaching the 

 margin. These folds entirely conceal the appressed, outer adambu- 

 lacral spines, which extend to the margins of the rays, but project 

 very little if at all beyond it, so that the margin is merely crenulated, 

 or divided into small blunt lobes by slight notches. The spiracles, 

 between the outer ends of the webbed adambulacral spines, are ovate 

 pores, sometimes closed by an ovate operculum ; but in other cases 

 they are occupied by a small group of two or three short, papula-like 

 organs. 



" The jaws are surrounded by a marginal group of long, slender, 

 webbed spines, of which there are about four or five on each side; 

 the two innermost are somewhat the larger. On the actinal side of 

 the jaws there are also two much larger, isolated epioral spines, one 

 on each plate; these are entirely covered by a thick skin; when this 

 is removed the spine is flattened, tapered, and blunt at the tip, with 

 a rough surface, but not hyaline. 



" Color, in alcohol, dull purple. 



" The ambulacral feet are large and in two regular rows." 



The specimen described above as the type of P. hexactis was 

 taken oflf Newfoundland, in 57 fathoms, N. lat. 43° 05'. The type 

 of obscurus Perrier was from the Banks of Newfoundland, in 155 

 meters. The few Atlantic specimens have all been six-rayed, except 

 one seven-rayed specimen. It has also been taken at Spitzbergen and 

 Greenland. 



