ARCTIC SEA TO THE WEST OF GREENLAND. 15 



greater length of the alimentary canal and the longer and more attenuated generative 

 sacs, are results which may not unnaturally be expected to arise when the distribution 

 of the forms compared is kept in mind. 



Distribution. 



a. Greenland : Godhavn, lat. 69 14' N. (' Valorous ' Exped. & Hayes s Exped.), 

 the most northern locality on record. 



b. North of American Continent: Labrador, 10 fms., sandy bottom (Packard, fide 

 Verrill) ; Grand Manan (Stimpson) ; Eastport, under stones at low water (Verrill). 



? Sitcha (under the name of C. discolor, Eschscholtz). 



c. North of European Continent'. Finmark and Lofoten, 1-2 fms., sand (Sars). 



d. North of Asiatic Continent : Ochotsk Sea 1 (under the name of C. discolor, 

 Grube, Middendorff's Exped.). 



Description of the Illustrations of this Species on Plate I. 



Fig. 14. The animal, much contracted : natural size. 



15. Generative tubes : magnified. 



16. Portion of the mouth-ring : magnified. 



17. The pyriform infundibular organs or " Wimpertrichter : " magnified. 



18. One of the wheel-like spicules : magnified. 



19. One of the sacculi, to show the aggregation of the spicules : magnified. 



MYRIOTROCHUS RINKII, Steenstrup. Plate I, Figs. 20-24. 



1851. Myriotrochus Binkii, Steenstrup, Vid. Meddel. N. Forening i Kjobonhavn, 1851, p. 55, pi. iii. 



figs. 7-10. 



1852. Chiridota brevis, Huxley, Sutherland's ' Journal of a Voyage,' Append, vol. ii. p. ccxi. 

 1857. Myriotrochus BinJcii, Liitken, Vid. Meddel. N. Forening i Kjobenhavn, 1857, p. 22. 

 1863. Myriotrochus Binkii, Stimpson, Proc. Acad. Nat. Sci. Philad. 1863, p. 142. 



1867. Myriotrochus BinJcii, Selenka, Zeitsch. f. wiss. Zool. Bd. xvii. p. 367. 



1868. Myriotrochus Binkii, Semper, Reisen im Archipel der Philippinen, Holothurien, p. 24. 



1877. Myriotrochus Binkii (?pars), Theel, Nova Acta Keg. Soc. Sci. Upsal. ser. 3, 1877, no. xvii. p. 3. 



Body cylindrical, and tapering only slightly towards the posterior extremity, in 

 some specimens the middle portion being somewhat swollen out, which causes the Holo- 

 thuroid to present a slightly arched profile. Anterior extremity very broad and 

 incapable of being retracted within the body, the habit of the animal being compara- 

 tively short and thick, the length not more than four or five times the thickness. The 

 skin is smooth and whitish grey, and in some examples semitransparent, in which case 

 the five longitudinal muscular bands as well as some of the internal organs are visible 

 through the membrane. The surface of the body is overstrewn with large calcareous 

 wheel-shaped spicules of characteristic form, attached to the integument by means of a 

 short peduncle or prolongation of the skin, which is affixed to the central portion or 

 " boss." This, however, is not easy to be seen in all the spicules, as some are closely 

 appressed to the body, in consequence no doubt of muscular contraction. The spicules, 

 as a rule, are more numerous upon the dorsal than upon the ventral surface ; in some 



