REPORT ON THE HOLOTHUPJOIDEA. 119 



double row is often not very plainly marked, and now and then there is only a single 

 though slightly irregular row distinguishable. The pedicels in the inner row being fewer 

 in number and smaller in size than those in the outer row seem to be developed subse- 

 quently; and this fact becomes most evident on examining very young individuals in which 

 the inner pedicels are usually rudimentary, while those in the outer row are well developed. 

 The dorsal surface is supplied with processes which in most cases strikingly 

 differ from the pedicels, but which sometimes, as, for instance, in Benthodytes 

 sangninolenta (PL XLII. fig. 6) and Benthodytes typica (PL XLIV. fig. 8) resemble 

 the pedicels in Pedata by their smallness and cylindrical shape as well as by then- 

 capability of being entirely retracted within the body, but it must be remembered 

 that their rounded terminal part is without the characteristic disk-like sucker with its 

 supporting calcareous plate. It is of great importance to pay special attention to the fact 

 that — though the difference between the ventral and dorsal ambulacral appendages 

 is generally so plainly marked that no further explanation is necessary with regard to the 

 two terms " pedicels" and " processes" — a transition, nevertheless, is found between them, 

 consequently, no definite limit can be marked ; however, their functions being unques- 

 tionably diverse, the use of different terms is fully justified. Even those Elasipoda which 

 carry on their dorsal surface small foot-like appendages never use the rounded, convex 

 dorsum for the purpose of locomotion, but move forwards on their flat, ventral surface, 

 which becomes fully evident when we consider the position of the mouth, &c. Thus it 

 would be inaccurate to term these foot-like dorsal appendages pedicels, which, being 

 present only in a few forms, are most certainly just as inapplicable for the purpose of 

 locomotion as the large dorsal processes or appendages. 



The dorsal ambulacral appendages are either simple or compound ; the former 1 

 prefer to call processes, and the latter appendages. Both kinds are often found in 

 the same animal, and vary considerably in size as well as in form and position. 



The processes are regularly more or less elongated, conical, and sometimes tuber- 

 culous, and often attain a size so considerable as not to admit of being retracted within 

 the body, excepting in the genus Ilyodcemon, which seems to have all the dorsal processes 

 completely retractile, which is probably owing to their communication with true ampullae 

 (PL XLII. fig. 3). In the Dehnatidge the processes attain the greatest size, and it 

 ought to be specially pointed out that Oneirophanta mutabilis and Lcetmogone ivyville- 

 thomsoni carry processes of the same length as the body itself, thus reaching a length of 

 125 mm. or more. The processes are in general more or less flexible, but in certain 

 forms, as, for instance, in the two species of Deima, they are very stiff and directed straight 

 out from the body, thus bearing a resemblance to gigantic spines. Sometimes, as in 

 Parelpidia, the processes are extremely minute, almost rudimentary. I have recently 

 drawn attention to the small foot-like and completely retractile processes in Ben- 

 thodytes sanguinolenta and Benthodytes tyinca. 



