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



between them is totally wanting. There are two polian vesicles, one on each side of the 

 ventral surface ; their length is rather inconsiderable, only 7 or 8 mm. The madreporic 

 canal penetrates the body-wall and opens externally by a pore, situated a little in front of 

 the genital aperture ; its parietes contain only a few scattered spicula, but the body-wall 

 round its aperture is provided with large close-set, four-armed, more or less irregular 

 calcareous deposits. The cloaca is small and insignificant. The reproductive organ 

 consists of two large, wide tubes, which communicate anteriorly with a narrow efferent 

 duct which opens at the top of a very small papilla placed immediately above the 

 downwardly directed neck-part of the body. The said tubes bear scattered thin bundles 

 of rather large, elongated csecal sacs. 



Elpidia incerta, n. sp. (PI. VIII. fig. l). 



Body elongated, about twice and a half as long as broad, considerably depressed 

 posteriorly. Mouth anterior, ventral. Anus posterior, dorsal. Tentacles large, of almost 

 equal size, some of the dorsal ones a little smaller ; their terminal part very large, 

 circular and discoidal, with numerous small retractile processes. The dorsal surface with 

 a pair of indistinct, tuberous processes at its foremost part. Pedicels ten, all along each 

 side of the ventral surface, rather large, the posterior pair a little smaller. Integument 

 thin, slightly rough and transparent, containing calcareous deposits, composed of four 

 arms and two to four processes, resembling those of the preceding species. 



Colour in alcohol, white. Length, about 90 mm. Breadth, about 27 mm. 



Habitat.— Station 152. February 11, 1874. Lat. 60° 52' S., long. 80° 20' E. 

 Depth, 12G0 fathoms ; diatom ooze. Four incomplete specimens. 



This species seems to be most closely allied to Elpidia willemoesi ; the four 

 individuals brought home by the Challenger expedition differ indeed so slightly 

 from it, that I have long been in doubt whether it is justifiable to refer them 

 to a new species or not. The body has its greatest height, about 20 mm., 

 anteriorly and thence it diminishes gradually backwards, the hindmost extremity 

 becoming thus very thin. Anteriorly, where the body attains its greatest height, the 

 dorsal surface bends rather abruptly downwards, forming a kind of rounded hump, 

 whereby the neck-like narrow portion of the body, which supports the mouth and 

 the tentacles, seems to have an almost perpendicular direction ; thus the mouth has a 

 thoroughly ventral position. The tentacles — only six are left in one specimen, and they 

 are altogether torn off from the other three individuals — do not seem to be of quite equal 

 size, a couple of the dorsal ones being a little smaller. Their terminal part is uncom- 

 monly large, circular, flat, and discoidal. The pedicels resemble in size and position 

 those of the preceding species, excepting that here the first pair is placed a little 

 further from the tentacles. The back bears only two tuberous indistinct projections, 

 lying side by side, and situated just on the above-mentioned hump ; they are so 



