REPORT ON THE HOLOTHTTRIOIDEA. 33 



Habitat— Station 325. March 2, 187G. Lat, 3G° 44' S., long. 46° 16' W. Depth, 

 2650 fathoms; bottom temperature, - 4° C. ; grey mud. One specimen. 



The mouth is almost terminal, slightly bent towards the ventral surface, and is 

 surrounded by tentacles of almost equal size ; their terminal part, a little smaller than 

 that of Scotoplanes mollis, is furnished with numerous retractile processes, and with a 

 slight incision in its outer margin. Of the pedicels six pairs are of a conical form 

 with a rather large base ; whether the others, which are very small and insignifi- 

 cant, form two pairs or one only is difficult to decide, but I have thought the 

 former to be the case. The transverse ridge on the dorsal surface is very low, 

 crossing the odd interambulacrum from one radius to the other, and bears four small 

 processes, of which the two in the middle are larger than the others, which are almost 

 inconspicuous. Close behind this ridge each ambulacrum is provided with a minute 

 process. The integument, very thin and transparent, is covered with papillae of a 

 more considerable size than those of Scotoplanes mollis. The ventral surface seems to 

 be almost destitute of such papillae. The calcareous deposits resemble those of the 

 above-mentioned species ; however, the C-curved ones seem frequently to be provided 

 either with a small straight spine issuing from the middle or with a long curved 

 arm, constituting thus a three-armed figure. The straight spicula are generally smaller 

 on the ventral surface than on the dorsum, some of them being comparatively small 

 and without spines. 



From want of material, I have not been able to study more in detail the calcareous 

 ring ; it is only possible to state that it is composed, as usual, of five pieces (PI. 

 XXXVII. fig. 12), each consisting of a central part, from which radiate eight rather straight 

 rods. But I have not been able to decide positively whether those pieces are separated 

 from each other, or whether they are united by the ends of the rods, thus forming a 

 perfect ring ; I suppose the former to be the case. The polian vesicle is minute. The 

 madreporic canal opens externally, 9 mm. behind the crown of tentacles. The re- 

 productive organ consists of a single, rather large fascicle made up of a great many 

 small close-set caeca. 



It is obvious that the three forms Scotoplanes globosa, S. mollis, and S. pap>illosa 

 are closely allied, and one is scarcely able to detect in the forms of the calcareous 

 deposits any character to distinguish them from one another. On the contrary, trie 

 size, the position, and the form of the dorsal processes present, I believe, very good 

 and constant specific characters. Scotoptlanes globosa differs greatly from the two others 

 in the form of the body, which, in consequence of the unusual convexity of the 

 dorsal surface is more or less distinctly globular, while the body of the other two species 

 is considerably more elongated. 



(ZOOL. CHALL. EXP. PART XIII. — 1881.) N 5 



WOODS 



Wfil F 



