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



six very soft and flexible processes disposed in an almost transverse row on its anterior part. 

 Integument very thick, soft, spongy, and apparently porous ; calcareous deposits com- 

 posed of three more or less spinose arms, each arm with a process near the common 

 central point. 



Colour in alcohol light grey, inclining to green. Length, about 100 mm. Breadth, 

 about 50 mm. 



Habitat.— Station 241. June 23, 1875. Lat. 35° 41' N., long. 157° 42' E. Depth, 

 2300 fathoms; bottom temperature, 1'1° C. ; red clay. Two specimens. 



When preparing the Preliminary Eeport on the Holothuridse of H.M.S. Challenger, 

 I had not an opportunity of making a detailed examination of the perisoma of this 

 species, and as it was quite impossible to detect any traces of calcareous deposits either 

 by a microscopic examination of small pieces of the integument or by treating them with 

 a solution of potass, I took for granted that there were none. By using such colouring 

 matters as haematoxylin, however, I have been persuaded that I made a mistake in 

 stating that the perisoma was destitute of deposits. This reagent brings out with such 

 distinctness the extremely thin sheaths or membranes which surround the calcareous 

 deposits, that one gets a fairly true idea of their forms, though the calcareous matter has 

 been dissolved for a considerable time. On account of this I have thought it necessary 

 to change the name of the species so as to avoid the chance of misapprehension. 



The dorsal surface is extremely convex, the ventral, on the contrary, is almost flat 

 or slightly concave. An obvious edge marks the transition between these surfaces. The 

 body is especially broad posteriorly and rounded in the form of a semicircle, and de- 

 creases anteriorly towards the crown of tentacles where it is almost truncated. The 

 mouth, the surrounding oral disk, as well as the tentacles, are almost terminal, 

 being slightly inclined towards the ventral surface. The anus is of considerable size, 

 and is situated on the dorsal surface, about 17 mm. from the sharp edge which 

 separates the ventral and dorsal surfaces posteriorly. The left side of the extremely 

 convex dorsal surface is divided into large rhomboidal or quadrangular prominent 

 areas, separated from each other by furrows ; these have been caused by abnormal 

 contraction, though it may appear very peculiar that both of the specimens should 

 possess them. The tentacles seem to be of almost equal size, some of the ventral or 

 dorsal ones being slightly smaller. Their large, discoidal ends, projecting beyond 

 the supporting stems, are provided with a number of very small, retractile processes, 

 especially round their margin. The ventral surface bears thirteen pedicels all along its 

 sides and an odd one posteriorly, in the middle, the first pair projecting near the ten- 

 tacles. Most of them are retracted, but a few which are in a state, of extension indicate 

 that they are rather short, with their terminal part large, flat, and slightly convex. About 

 35 or 40 mm. behind the crown of tentacles the dorsal surface supports about six conical 

 processes, which are arranged in an almost transverse row, and attain the length of about 



