KCHINOIDEA. I. 129 



ran Bnniti Ag., viridis Ag., and macrostonia (Ltk.). Whether the last-named one is a genuine Ecliino- 

 inctra cannot be decided for the present, as only naked tests and loose spines are known. The other 

 species agree in the main features, also with regard to pedicellarise and spicules; so there is no reason 

 to enter into details with regard to the separate species, only a few features characteristic of the genus 

 are to be mentioned. A primary tubercle is found on all the ambulacral plates; no ocular plate reaches 

 to the periproct in Ech. oblonga and viridis, while in lucunter generally one plate, rarely two or none 

 at all reach to it. The buccal membrane contains numerous large, but fine fenestrated plates, almost 

 all without pedicellarise. Spines on the buccal plates. The globiferous pedicellarise have one unpaired, 

 strong lateral tooth, as Perrier has pointed out, and he has figured it in an excellent manner 1 ). There 

 is no neck; the stalk is compact. In E. oblonga is found the peculiarity that the stalk has a joint in 

 the middle; in E.vanBrunti the globiferous pedicellariae are very small, but otherwise of the common 

 form. The tridentate pedicellarise are narrowly leaf-shaped with little developed mesh-work (see Rev. 

 of Ech. PI. XXVI. Figs. 9, 1213); in van Brunti they are of a quite different form, short, narrow, 

 a little widened in the point, and the blade quite filled by a complicate mesh-work (PI. XIX, Fig. 21). 

 The ophicephalous pedicellarise with a rather strong mesh-work, a little different in form, although 

 upon the whole of the common structure; the triphyllous pedicellariae of the common form. The 

 spicules bihamate. 



The genera Hctcrocentrotus, with the species mamillatus (Klein) and trigonarius (Lamk.), and 

 Coloboccntrotus, with the species atratus (L.) and Mcrtensu Bi. are most nearly allied to Echinoiiietra, 

 as is commonly supposed; the globiferous pedicellariae and the spicules are chiefly as in this genus. 

 A primary tubercle is found on all the ambulacral plates; no ocular plate reaches to the periproct. 

 The buccal membrane with numerous fenestrated plates several of which carry pedicellariae and small 

 spines as the buccal plates. The gills are in Heterocentrotus uncommonly well provided with fenes- 

 trated plates some of which even carry (triphyllous) pedicellariae; rather numerous small bihamate 

 spicules are also found among the fenestrated plates. In Coloboccntrotus fewer fenestrated plates are 

 found, but also here they carry triphyllous pedicellarise. -- Only in these two genera I have seen this 

 peculiar feature that pedicellarise are found on the gills. - - In Colobocentrotus the globiferous pedicel- 

 larise are quite small and placed quite down among the flat spines on the abactinal side; the edges 

 of the blade not connected by cross-beams (PI. XIX. Fig. 5). The stalk is curved. (In C. Mertensii 

 I have not seen the globiferous pedicellarise.) Of the tridentate pedicellarise in Heterocentrotus 

 Agassiz (Rev. of Ech. p. 665) has the remarkable expression that the tridactyle pedicellariae are of 

 the type called trifoliate*. I do not understand the sense of this expression; otherwise a rather good 

 figure is given of these pedicellariae in //. mamillatus (XXVI. Fig. 2). There is a striking difference 

 between the tridentate pedicellarise in mamillatus and trigonarius. In the former (PL XIX. Fig. 15) the 

 blade is narrow in the lower part, widened at the point, with a pair of rather projecting corners; the 

 valves only join at the point, and are otherwise wide apart; in trigonarius the blade is of the common 

 leaf-shape (PL XIX. Fig. 35), with no widening at the point, and the valves join through their whole 

 length. In both of them the edge is very slightly serrate, but there are some larger indentations in 

 the narrow part of those of mamillatus. Perrier (op. cit.) thinks that several fftefOCntr0tt 



>) Rech. sur les Pedicellaires etc. PI. VI. 

 The Ingolf-Expedition. [V. i. 17 



