ECHINOIDEA. II. 



47 



(Panamic Deep-Sea Ecli. p. 163) to the genus Pilemat echinus established there for Cystech. Rathbuni. 

 - A few remarks on the forms mentioned above may be given here. 



Cystechinus clypcatus. In the description of this species (^ChalLs-Ech. p. 149) Professor Agassiz 

 remarks that in the specimens from the greater depths (ca. 1900 fathoms) the test is much thinner 

 than in the fragments which are found near the 1000 fathom line;>. This may perhaps be true for 

 other species (Agassiz refers to Pourtalcsia, Cystechinus and Ur echinus], though I do not see any 

 such difference among the specimens of U. naresianus from the clngolf*; but as for C.clypeatus the 

 difference in the thickness of the test is in any case not alone due to the different depth at which 

 the specimens lived, but also to their being different species, as I can state after having examined 

 the fragments preserved in the British Museum; the pedicellarise differ so considerably that it seems 

 quite impossible that they can belong to the same species. Also the structure of their apical sys- 

 tems will probably be found to differ considerably. In the description it is said: The abactinal 

 system closely resembles that of Cystechinus Wyvillii; the genital plates are, however, proportionally 

 larger, the left anterior and the right posterior far exceeding the others in 

 size, and extending entirely across the abactinal area, the whole central part 

 of which is formed by the junction of the genital plates*. But the figure, PL 

 XXXV. b. 10, is, as will be seen, not in accordance with that description ; the 

 left anterior and right posterior genital plates do not exceed the others in 

 size or extend entirely across the abactinal area, and the whole central part 

 is not formed by the junction of the genital plates, the large ocular plates 

 of the anterior paired ambulacra separating widely the anterior and posterior 

 genital plates. Among the fragments of Cystechinus clypeatus preserved in 

 the British Museum the apical system is found in those from St. 334, which Fi Apical s stem of 



belong to the thin-plated form. This apical system does not agree, however, Cystechinus clypeatus (St 



334)- 

 either with the description or the figure (PI. XXXV. b. 10) as will be seen from 



the sketch given here (Fig. 5). (It may be remarked that this figure was made free hand, without a 

 camera, so that the form of the plates may not be quite correct, but in the main features the figure 

 is correct.) In the fragments from St. 133, which evidently belong to the same species as those from 

 St. 334 (both these stations are near Tristan d'Acunha), only the two posterior apical plates, together 

 with some of the plates behind them, are preserved; this part agrees with the figure in the Chal- 

 lenger -Echini, which thus seems to have been made after this specimen. Whether the whole figure is 

 correctly drawn can no longer be seen. - - Among the fragments from St. 205 (off Luzon, in the China 

 Sea) 1 , the thick-plated form, no trace of the apical system is found. 



On the fragments of the thick-plated form (St. 205) I have found three kinds of pedicellarise, 

 viz. tridentate and two kinds of ophicephalous pedicellarise. Unfortunately, no globiferous pedicellariae 

 were found; they will probably also be very characteristic, as is the case with the ophicephalous. The 

 tridentate pedicellarise (PI. IX. Figs. 14, 28) have a simple, leaf-shaped blade, somewhat narrowed in the 

 lower part. The edge is thick, only faintly serrate, often with a larger tooth at the point; in the larger 

 ones there is, generally, a wingshaped lateral widening below the edge in the lower part of the blade. 



1 Alone this very wide distance between the stations might beforehand raise some doubt of these forms being the 

 same species. 



