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



The general relations of these seven genera of Comatulidse are expressed in the 

 following table : — 



I. Centro-dorsal has no articular facet on its lower surface. 



A. Five rays. 



i. Mouth central or subcentral. Oral pinnules have no comb. 



a. Kadials separated by interradials, . . . . 1. Thaumatocrinus, n. gen. 



b. Radials united laterally. 



(1) Basals persist as a closed ring. No pinnules on 



lower brachials, . . . .2. Atelecrinus, n. gen. 



(2) Basal ring incomplete or invisible externally. 



a. Five arms only, . . . .3. Eudiocrinus, Carpenter. 



j3. Ten arms, . . . . .4. Antedon, de Freminville. 



ii. Mouth excentric or marginal. Oral pinnules have a terminal 



comb, . . . . . . .5. Actinometra, Miiller. 



B. Ten rays, . . . . . . . .6. Promarhocrinus, n. gen. 



II. Centro-dorsal has an articular facet below, . . . . .7. Tldolliericrinus, fitallon. 



Genus 1. Thaumatocrinus, P. H. Carpenter, 1883. 

 1883. Thaumatocrinus, P. H. Carpenter, Phil. Trans., 1883, pt. iii. p. 919, pi. lxxi. 



Definition. — Calyx composed of a centro-dorsal, basals, radials, and primary inter- 

 radials, the latter resting on the basals and so separating the radials laterally. That on 

 the anal side bears a short jointed appendage. Mouth central and protected by five 

 large oral plates which occupy the greater part of the disk, and are separated from the 

 calyx-intei'radials by two or three rows of small irregular plates. Five arms only. 



Remarks. — Thaumatocrinus has already been described and its peculiarities discussed 

 in Part I. of this Eeport (pp. 370-372), and it is not necessary therefore to refer again to 

 the reappearance of certain Palseocrinoidal characters in this remarkable genus. As 

 compared with the more typical Comatulse it is peculiar in having persistent basal and 

 oral plates, the latter occurring in no other Comatulid, and in the simplicity of the rays, 

 which remain undivided, so that there are only five arms, as in Eudiocrinus (PI. VII.). 



Thaumatocrinus renovatus, P. H. Carpenter, 1883 (fig. 1; Part I. pi. lvi. figs. 1-5). 



Description of an Individual. — The total width of the calyx across the disk is barely 

 2 mm.; and the height of the centro-dorsal and radials together is about the same. The 

 former is rounded below, with its central canal completely closed up, so that it must 

 have been detached for some little time from the remainder of the stem. The bases of 

 half a dozen cirri are attached to it, and there are pits for the reception of two or three 

 more. In the largest stump which is preserved the first two joints are quite short, as is 

 usually the case in all cirri ; but the third reaches a length of 1"5 mm., so that the cirri 

 must have been very like those of some species of Eudiocrinus, which have a succession 

 of very long joints followiug the short basal ones (PI. VII. figs. 2, 7). 



