REPORT ON THE HOLOTHURIOIDEA. 



117 



or, finally, decreasing to a narrow, tube-shaped, retractile prolongation, as, for instance, 

 in Elpidia glacialis, &c. But as a matter of fact a strict separation of these pedicels 

 into two groups is not possible, the interval between them being filled up by a series of 

 gradations. Both kinds of pedicels differ from those in the Pedata by the notable 

 peculiarity that they show no traces of a calcareous terminal plate j 1 the genera llyo- 

 dcemon and Lcetmogone are most singular exceptions to this, having the ends of their 

 pedicels supported by one or more perforated plates. In the Psychropotidse, which in 

 many respects may be regarded as intermediate between the true Elasipoda and the 

 Pedata, the pedicels, having lost much of the typical form characteristic of the deep-sea 

 Holothurians and evidently approaching those in the Pedata, belong to the first, that is 

 to say, to the small kind. Some of these pedicels are more or less minute, and are 

 arranged in a double row all along the odd ambulacrum ; others are sbghtly larger and 

 form a single row round the margin of the brim of the body. The large cyhndrical 

 pedicels which, on the contrary, are present in the other two famibes, are disposed in a 

 single row along each of the lateral ambulacra on the ventral surface. As the only known 

 exceptions I may cite Oneirophanta mutabilis and Ilyodcemon maculatus in which the 

 pedicels in question are disposed in a double alternate row along each side of the ventral 

 surface, whde the first-mentioned species as well as the genus Pannychia are the only 

 forms excepting the family Psychropotidas which carry pedicels on the odd ambulacrum, 

 the former carrying few, the .latter many. As above mentioned, only a comparatively 

 small number of the Elasipoda have all three ambulacra provided with pedicels, while 

 the majority carry along each side of the ventral surface only a single row of large 

 cylindrical, locomotory pedicels. These large pedicels, which are to be regarded as direct 

 protuberances of the body-wall are often strengthened by calcareous deposits, more or 

 less closely resembling those in the perisoma in form as well as in number. Thus, for 

 instance, if the body-wall itself is firm and brittle, as in Oneirophanta, Deima, &c, 

 the pedicels also become highly brittle and inflexible. In order to give an idea of the 

 size of these larger pedicels I refer to the following list : — 



Here I may again refer to the peculiarity, which has already been mentioned in my 



1 Special attention should be paid to what has been pointed out in the description of species given above, that various 

 representatives, especially in the Psychropotidse, for some reason or other possess no calcareous deposits, wherefore it is 

 possible — though not probable — that in these very animals calcareous terminal plates should have existed supporting 

 the ends of the pedicels. 



