KCHINOIDKA. 11. 47 



(Panamic Deep-Sea Ecli. p. 163) lo tlie j^emis Pilematechinus established there for Cystech. Rathbuni. 

 — A few remarks on tlie forms mentioned aljove ma\- be j^iven liere. 



Cystechinus clypeatits. In the description of tliis species ( Chall. -Ech. p. 149) Professor Agassiz 

 remarks tliat in the specimens from tlie cj^-reater depths |ca. 1900 fathoms) the test is much thinner 

 than in the fragments which are found near the icxxj fathom line:. This may perhaps be true for 

 other species (Agassiz refers to Poiirtalcsia, Cystechinus and Urrchimis), tliough I do not see an\' 

 such difference among the specimens of U. uaresianus from the Ingolf ; 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 wliich 

 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 pedicellariae differ so considerabh- that it .seems 

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

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

 system closely resembles that of Cystccliiiins Uyvil/ii ; the genital plates are, however, proportionalh- 

 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 b\ the junction of the genital plates . But the figure, PI. 

 XXXV. b. 10, i.s, 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 entireh- 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 widel\' the anterior and posterior 

 genital plates. — Among the fragments of Cys/cc/iiiius chpfatus preserved in 

 the British Museum the apical svstem is found in those from St. ^^4, which _. ^ , . , 



' • J-J^^' Fig. 5. .\pical system of 



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

 either with the description or the figure (PL XXX\'. 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 evidenth' belong to the same species as those from 

 St. 334 (both these stations are near Tristan d'Acunha), onl\- 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 

 correcth' drawn can no longer be seen. — Among the fragments from St. 205 (off Luzon, in the China 

 Sea)', 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 pedicellarite. Unfortunately, no globiferous pedicellarise 

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

 tridentate pedicellariae (PL 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 .\loue this very- wide distance between the stations might beforehand raise some doubt of these forms being the 

 same species. 



