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



4. Pneumonoderma boasi, u. sp. (PI. II. fig. 3). 



188G. Pneumodermon violaceum, Boas (pars), Spolia atlantica, K. dansk, Yidensk. Selsk. Skriv., 



6 Kaekke, Bd. iv. p. 154. 



Body, head, and foot as in the two foregoing species. 



Lateral Gill short, with fringes not subdivided, and fringed lateral somatic crests. 



Posterior Gill with short radiating crests, of which the fringes are not subdivided, but 

 distinct, markedly separated, projecting and narrow at their base ; they number three on 

 each side of the radiating crests. 



Acetabuliferous Appendages bearing about forty small suckers, of the same shape as 

 those of Pneumonoderma mediterraneum. 



Hook-sacs rather short. 



Colour. — Brownish ; pigment existing as small spots visible to the naked eye. 



Length, 7 mm. (in a contracted state). 



Habitat. — South-East Pacific, off Caldera (Chili), about lat. 27° S. ; " Vettor Pisani" 

 Expedition, February 18, 1883. 



Observation. — A young specimen, about 4 mm. long, still showed well-marked traces 

 of the second ciliated ring of the larva ; the fringes on the branchial crests were not yet 

 formed. 



*5. Pneumonoderma pacificum, Dall (PL II. figs. 4, 5). 



1871. Pneumodermon pacificum, Dall, Descriptions of Sixty New Forms of Molluscs from the 



West Coast of North America, Amer. Journ. Conch., 

 vol. vii. p. 139. 



Body. — Head and foot like those of the other species of the genus. 



Lateral Gill long, with fringed lateral somatic crests. 



Posterior Gill with short radiating crests, of which the fringes are simple well-marked 

 foldings on each side of the crests, those of one side alternating with those of the other. 

 These fringes are close to one another, and the radiating crests being short, they are not 

 numerous. 



Acetabuliferous Appendages triangular, bearing about fifty small suckers of the same 

 shape as those of Pneumonoderma mediterraneum. 



Radula. — Formula 4 : : 4, in specimens 1 cm. long. 



Hook-sacs long. 



Colour. — Purplish-brown ; pigment chiefly abundant on the right side, and distributed 

 in small spots, visible with a magnifying glass. 



Length. — Dall 1 gives 1 inch as the maximum size of this species ; the specimens 

 from the Challenger Expedition are about 1 cm. long. 



Challenger Specimens. — Station 240, June 21, 1875; Yokohama to Honolulu; 

 lat. 35° 20' N., long. 153° 39' E. 



1 Amer. Journ. Conch., vol. vii. p. 140. 



