EEPOET ON THE HOLOTHUEIOIDEA. 11 



slightly retractile pedicels, disposed in a single row all along each side of that surface, 

 or round its posterior half, or only on the margin of a brim surrounding the hindmost 

 extremity of the body; the odd ambulacrum naked; the dorsal surface with a smaller 

 number of sometimes very long, sometimes rather short or nearly rudimentary processes 

 commonly disposed on its anterior part, or with a large branched or unbranched lobe-like 

 appendage, situated anteriorly or forming a brim round the foremost extremity of the 

 body ; calcareous deposits ; straight or slightly curved, C-shaped and horseshoe-shaped 

 spicula, three- or four- armed bodies, more seldom a few minute, net-bike plates, minute 

 wheels, rosette- shaped or elliptical bodies ; calcareous ring composed of only five spicule- 

 shaped pieces, each consisting of a number of long, slender rods, diverging in opposite 

 directions from a small central part. 



This family presents a great number of forms of the most variable appearance. At 

 first sight it seems almost impossible to comprise under the same family two genera so 

 different from one another in their external appearances as, for instance, PareVpidia and 

 Peniagone, but, after comparing all the thirty-one forms with one another, those scruples 

 vanish totally, and give place, on the contrary, to some difficulty in finding satisfactory 

 generic characters. The interval between those two extreme forms is filled up by such a 

 series of gradations as to make a strict definition of the genera rather troublesome. 



In defining the genera of this family, we have in the first place to consider the 

 number of the tentacles, which, as characteristic of the family, may be regarded as 

 being ten, only three forms being exceptions to this rule : Enypniastes eximia, 

 Achlyonice paradoxa, and Achlyonice lactea, the first of which has about twenty 

 tentacles, and the two latter only eleven or twelve. Enypniastes being an extremely 

 characteristic form, and greatly different from the other genera of this faniilv, I have 

 felt somewhat doubtful with regard to its place in the system ; its unexpectedly great 

 number of tentacles, and several other peculiarities indicate a closer alliance with the 

 family Psychropotidae, but the individuals which have been at my disposal were in such 

 a lacerated condition as to render it impossible to state anything concerning them. 

 Likewise, on account of the number of its tentacles, I believe the genus Achlyonice to be 

 justified. Achlyonice paradoxa being the typical form, seems, by its constant twelve 

 tentacles, by the form of its body, and by other distinctions, to be easily distinguished 

 from other genera, while the other species, Achlyonice lactea, having either eleven 

 or twelve tentacles, approaches more to the genus Elpidia. Besides, the genus in 

 question mayeasdy be discerned by its calcareous bodies. In addition, I have tried to 

 find out suitable generic characters from the shape of the body, as well as from the forms 

 of the dorsal appendages, and, above all, from the construction of the calcareous deposits. 

 Parelpjidia differs from all other genera by its unusual length ; it bears some similitude 

 to the Synaptse in its narrow cylindrical shape, with the mouth and anus at the opposite 

 ends of the body, this resemblance being the more striking, as the dorsal surface is almost 



