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



naked, its few processes being very rudimentary. Consequently, this genus is represented 

 by forms which differ in their external shape most remarkably from the other Elpidiidse. 

 Notwithstanding this, a conformity not to be neglected really exists between them, in 

 the arrangement of the internal organs, as well as in the position of the pedicels and 

 the form of the calcareous deposits. It is worthy, indeed, of observation that the 

 four-armed deposits of Parelpidia always carry but one process, while the other genera, 

 Elpidia, Peniagone, and Scotoanassa, provided with similar calcareous bodies, always 

 seem to bear, besides those deposits with one process, numerous others having two 

 to five processes. It is possible that after the discovery of some new forms this 

 difference may turn out to be of little or no importance, but, in the present state of our 

 knowledge, it deserves to be kept in mind. The genus Scotoanassa seems to represent 

 the type of a new genus on account of its singularly depressed body, and the flattened 

 margins surrounding the anterior and posterior extremities. 



On the other hand, it might seem that too little attention is given to the shape of 

 the body by including animals of very different appearances in the genus Elpidia. 

 The difference between such forms as Elpidia glacialis and Elpidia verrucosa on the 

 one side, and Elpidia willemoesi on the other, is most conspicuous, this latter species 

 being distinguished partly by the flatness of the posterior end of the body, and partly 

 by the pedicels round this posterior end being webbed together by an extension of the 

 integument. If this peculiarity should call for a new genus, Peniagone vitrea and 

 Peniagone affinis, for instance, though closely related, for the same reason ought to be 

 separated from one another, the consequence of which would be, in our opinion, that 

 generic division was being urged too far ; possibly a separation into sub-genera might, 

 on account of what is mentioned, be justified. I have felt somewhat doubtful whether 

 Elpidia glacialis, might not keep its place as the sole representative of the original 

 genus, thus necessitating a new genus for the remaining species, and I am of opinion 

 that this separation might be fully justified — particularly as the calcareous deposits 

 and the construction of the calcareous ring give plain evidence — if I were quite per- 

 suaded that Elpidia glacialis really is the only form in which the madreporic canal 

 does not communicate with the exterior. Fading this I feel obliged to leave the 

 definite decision of this point to further investigations. The dorsal appendages are 

 found to be of two different kinds, one having the form of larger or smaller, more or 

 less elongated conical processes, enclosing a single canal, the other, on the contrary, consist- 

 ing of a generally very prominent and broad lobe traversed by several canals. Parelpidia, 

 Elpidia, Scotoplanes, Kolga, Irpa, and Achlyonice carry appendages of the former kind, 

 while the three other genera of this family bear a dorsal lobe of greater or smaller dimen- 

 sions. The conical processes are usually situated on the anterior part of the dorsal 

 surface, though one pair or more are also to be found posteriorly, as, for instance, is the 

 case in Scotoplanes globosa, Scotoplanes murrayi, and Elpidia glacialis ; especially in 



