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



All the thirty-one known forms of the Elpidiidse seem to be characterised by having 

 the calcareous ring composed of only five spicules which are either firmly united 

 with one another, thus forming a pentagonal figure which surrounds the gullet as iu 

 Elpidia glacialis, or are more loosely combined with one another, by having the arms 

 of the spicules not lying side by side as in the preceding species, but only joined with 

 one another by their ends as is the case in Kolga hyalina, Dan. and Koren, or, lastly, the 

 spicules are separated at certain distances from one another, as is plainly shown in most of 

 the species. The various kinds of rings may with advantage be described more in detail. 



Each spicule which composes the ring consists of a short, insignificant central part, 

 from which a greater or smaller number of rod-like arms diverge towards each side ; 

 the ends of these are in general flat, enlarged, perforated and branched, but sometimes 

 simple, pointed, or slightly obtuse. In Elpidia glacialis each spicule consists of only 

 eight arms in all, two of which — viz., those two which are placed posteriorly and 

 internally when the ring is in its proper position — are large and, lying along their 

 whole length side by side and closely united to the corresponding arms of the adjacent 

 spicules, help to form a pentangular figure ; of the rest of the arms the posterior 

 outer ones join one another at their ends, and this sometimes seems to be the case 

 even with the anterior inner ones. A correct idea of the composition of this cal- 

 careous ring may be gained by referring to my report on the Elpidia. 1 According 

 to Danielssen and Koren 2 each spicule in Irpa abyssicola is likewise composed of 

 eight rod-like arms, four of which diverge towards each side, but judging by the 

 description and plates given of these authors, the combination between the separated 

 spicules cannot take place in the same manner as in Elpidia glacialis ; most probably 

 some of the arms reach or cross the corresponding arms of the adjacent spicules, thus 

 constituting a pentagonal ring. 



According to the observations of the same authors 3 each spicule in Kolga hyalina 

 gives off fourteen rods, seven of which diverge towards each side ; several of the posterior 

 rods, which are the longest, join their ends to those of the adjacent spicules, thus forming 

 a complete pentagonal ring. In all the eight or nine species of this family which I have 

 had the opportunity to examine, the five spicules are found at certain distances from one 

 another, consequently no complete ring is present. Each spicule in Scotoplanes globosa, 

 Scotoplanes papillosa (PL XXXVII. fig. 12), and Scotoplanes robusta (PI. XXXVII. 

 fig. 9) is made up of eight rods, of which four di verge towards each side. Peniagone 

 vitrea possesses spicules, which send out about sixteen rods, eight towards each side ; and 

 each spicule in Elpidia vrillemoesi (PI. XXXVII. fig. 1) and Parelpidia elongata 

 (PI. XXXVII. fig. 2) is remarkable for possessing as many as twenty or thirty rods. 



1 Memoire sui l'Elpidia (Kongl. Sv. Vet.— Akad. Hand]., Bd. xiv. No. 8, Stockholm, 1877). 



2 Echinodermer fra den Norske Nordkavsexpedition (Nyt Mag. for Naturvid., Bd. xxiv. 3). 



3 Echinodermer fra den Norske Nordhavsexpedition (Nyt Mag. for Naturvid., Bd. xxv. 2, 1879). 



