86 THE VOYAGE OF H.M.S. CHALLENGER. 



and twenty along the right side, while the other carries eighteen on the left and 

 nineteen along the right side ; consequently, the number of pedicels in this species 

 seems to be subject to considerable variation. All the pedicels, excepting the 

 foremost and hindmost ones, of the largest and most developed individuals are 

 evidently disposed in a double row along each side of the ventral surface, those of the 

 inner row alternating with those of the outer row ; this arrangement of pedicels in 

 double rows is less obvious in the younger animals. The pedicels reach a considerable 

 size, the largest being about 15 mm. in length and about 8 mm. in diameter at the 

 base. The dorsal processes of the largest individual are very numerous and disposed 

 in about four very irregular rows along each ambulacrum, though anteriorly 

 and posteriorly only two rows are distinguishable. This disposition of the processes 

 appears most plainly on examining their vesicles from the inside of the perisoma. A 

 narrow area along the middle of the back is destitute of processes except anteriorly 

 where a minute one is situated, the importance of which I shall discuss further 

 on. The individuals from Station 192 are distinguished from the others by 

 possessing only two rows of processes along each of the dorsal ambulacra. The 

 fusiform or conical processes are extremely flexible and of variable size, the largest 

 measuring about 35 mm. in length and 7 mm. in diameter at the base (PI. XLII. 

 fig. 3). 



The integument is very thick, and rather soft and pliable. The ventral perisoma 

 contains apparently nothing but small wheels (PL XXXVI. fig. 17) and dichotomously 

 branched bodies (PL XXXVI. fig. 18) ; the former are more numerous and closely- 

 crowded, while the latter are partly scattered, partly agglomerated, thus becoming visible 

 to the naked eye as larger and smaller white spots or dots. The deposits of the sides of 

 the body almost correspond with those of the ventral surface, except in the neighbourhood 

 of the dorsal processes where large scattered wheels are found. The dorsal perisoma 

 between the series of processes is supported by a great many large wheels, while the small 

 wheels and the dichotomously branched bodies are there fewer in number. The small 

 wheels measuring about 0"028 mm. in diameter resemble those in Lcetmogone, except 

 that the hole in the centre is larger, the nave forming consequently a slender ring, from 

 the inner edge of which commonly four minute rods run out ; the number of spokes is 

 generally twelve. The large wheels (PL XXXVI. figs. 12-15), from 0-14 mm. to 

 - 2 mm. in diameter, remind one likewise of those of the above-mentioned genus, the 

 felly as well as the spokes being however more strongly developed ; the spokes, nine in 

 number, are attached to the posterior inner portion of the felly, and a transverse section 

 of them presents almost the form of a triangle. The crown of those large wheels, 

 made up of six minute rods, rises from the inner margin of the nave and sends out 

 from its top a process of larger or smaller dimensions, which sometimes is simple as 

 in Lcetmogone, but often supports a triangular figure, the three acute corners of which lie 



