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



de la ressemblanee absolue de ces dix plaques alternes avec eelles qui forment le periprocte 

 des Oursins et que Loven a rapprocli^es, a leur tour, de eelles qui constituent le calice des 

 Crinoides, opinion que nous aurons prochainement occasion de discuter. L'identite de dis- 

 position des plaques dorsales des Caulaster avec eelles du calice de Crinoides est evidente." 

 It would appear, however, from tlie foregoing description that Perrier's comparison of 

 the plates round the dorsal appendage of Caulaster with those forming the periproct of 

 an Ui'chin cannot be followed out in detail. The first row of plates in Caulaster, if 

 radially situated as Perrier states, cannot correspond to the first or inner row of the 

 apical system of an Urchin ; for these last are the genitals, and are situated interradially. 

 Their homologues are the plates in the second row of Caulaster, which alternate with 

 those of the first ; while the second ring of plates in the Urchins, the oculars or true 

 radials, appear not to be represented in Caulaster. If Perrier's description of the positions 

 of the plates in this type be correct, its apical system consists, not of genitals and oculars 

 (basals and radials) as in an Urchin, but of under-basals and basals ; and the true radials 

 must be so small as to have escaped his notice. 



NOTE B. 



(Page 36.) 



On the Basals of Fossil Comatul.^. 



In certain fossil Comatulse the ends of the basals are visible on the exterior of the 

 calyx between the radials and the centro-dorsal. They are sometimes quite small, as in 

 some forms ot Pentacrimis decorus (PI. XXXIV. fig. 1 ; PL XXXV. figs. 1,2; PL XXXVI. 

 fig. 3) ; while in other species, such as Solanocrinus scrobiculatus, Miinster, they may 

 reach a considerable size. As long as basals were supposed to be absent in the calyx of 

 the recent Comatulse, their presence in fossil forms appeared to be a character of generic 

 value. But after the discovery by Dr. Carpenter and Sir Wyville Thomson that the 

 Pentacrinoid larva has true basal plates which eventually become metamorphosed into 

 the concealed rosette, this distinction between the recent and fossil Comatulse no longer 

 holds good. Schluter^ recognised this fact in 1878, and pointed out that Solanocrinus 

 was merely a synonym of de Freminville's name Antedon. He referred to this genus 

 both Solanocrimis costatus, Goldfuss, and Solanocrinus scrobicidatus, Miinster, together 

 with two other fossil species, in both of which the basals appear on the exterior of the 

 calyx. Zittel,^ however, regarded Solanocrinus as a subgenus of Antedon, distinguished 

 from it l)y the presence of external basals. 



In the following year^ the examination of a considerable number of fossil Comatulse 



' Zeitschr. d. dcutsch. geol. Geselkch., Jahrg. 1878, pp. 36, 40. ^ Pateontologie, vol. i. p. .396. 



2 On some undescribed Comatulai from the British Secondary Rocks, Quart. Journ. Gcol. Soc, vol. xxxvi. 

 pp. 36-46, 1880. 



