ARCTIC SEA TO THE WEST OF GREENLAND. 11 



the size of the others. The scales are densely covered with very large granules, but 

 which in old specimens are not unfrequently abraded in places. 



The integument of the ventral area, although thin, is tough and leathery, and 

 presents no asperities to the touch. The ambulacral feet are entirely confined to the 

 ventral area, and are limited to its extreme outer margin, round which the suckers 

 form a broad border about four or five rows deep, very closely crowded, and having 

 no perceptible order in their arrangement except in the outermost series, which are 

 smaller than the rest, and form a line parallel with the margin. At the anterior and 

 posterior ends of this oval marginal series may be found a few additional suckers 

 extending along the median line : these are the rudiments of the aborted middle 

 ^ambulacral series ; and it is rare that more than four or five rows of four suckers each 

 are present. 



The mouth-ring resembles that of P. squamatus, D. & K., the elements having 

 more or less the form of an inverted Y, and the five interradial pieces being smaller 

 than the radials. 



The Polian vesicle is large and single, the generative tubes extremely numerous 

 and extensive, and the muscular system much more strongly developed than in 

 P. squamatus (Lu'tken). 



Respecting the spicules which occur in the cuticle of this Holothuroid, those of 

 the ventral skin are indefinite in shape, and are more correctly described as calcareous 

 reticulations having large circular apertures than as plates punctured with holes. 

 Short prolongations frequently rise at right angles from the decussations or midway on 

 the intercalary portions ; and occasionally secondary branchings are formed from these. 

 Here and there small cup-shaped spicules are to be met with, probably undeveloped 

 stages of the larger spicules. The tubes of the sucker-feet are overlaid with spicules 

 somewhat similar in shape and character to those of the ventral cuticle; and the 

 extremity is provided with a large circular calcareous disk, likewise of reticulated 

 structure, with the holes very large, close together, and nearly equal in size. 



Colour and Size. Psohis Falridi is, when alive, of a dark red colour, which 

 in spirit becomes changed to brown. Ayres speaks of his American specimens as 

 being of a bright brick-red when alive (loc. cit. p. 36). One of the largest examples 

 measured 3^ inches in length and over 2 inches in breadth (Lutken). 



Premature Form. In a young state the dorsal surface is more depressed, and the 

 orifices of the alimentary canal are somewhat nearer the margin than in the adult 

 animal. The ambulacral feet are limited to a double row of suckers surrounding the 

 margin of the ventral area ; and no trace is visible of the median series. It is of 

 interest to note that at this stage the young of the present species are almost undis- 

 tinguishable from those of Ps. pliantapus of a corresponding period of growth, although 

 the latter is a form whose habit differs most strikingly from that of the present species 

 when adult examples are compared. The same remark holds good for the young stages 

 of Ps. squamatus as well, the superficial differences at an early phase being nothing 

 more than slight variations in the character of the spicules that indurate the ventral 

 cuticle. 



c2 



