I2 6 ECHINOIDKA. II. 



Agassiz (Rev. p. 666) rightly refers this form to the tridentate form, though I might not strictly call 

 them ordinary tridactyle which is better said of the form with the slender valves. Koehler (217) 

 follows Perrier in regarding them as ophicephalous pedicellariae. 



The ophicephalous pedicellariae (PL XVI. Fig. 6) are generally few in number and have only 

 been found on young specimens; probably, however, it would also be possible to find some few 

 among the small abactinal spines in larger specimens; they are found only on the abactinal side and 

 in the posterior ambulacra on the actinal side. The valves are rather elongate, very narrow above the 

 articular surface, the side parts of the basal part being very small ; the blade widens towards the point 

 which bends inwards; rather strong teeth along the edge, continuing along the sides of the apo- 

 physis almost down to the articular surface. The blade is deepened in the middle part, with very few 

 holes and no keel continuing over it from the apophysis. There is a small process from the bow 

 which is the outermost of the three. There is no neck, and the upper end of the rather compact stalk 

 is cupshaped. 



The triphyllous pedicellariae (PI. XVI. Figs. 2, 22) are very small and delicate (the head ca. o-ia" 1111 

 long). The valves are simply leafshaped, the basal part being a little narrower than the blade, whose 

 lower corners are rather sharp; the edge is finely serrate on a small part at the lower end. On the 

 outer side there is a slightly prominent keel at the lower end. — This kind of pedicellariae has first 

 been seen by Koehler; what Agassiz mentions as < typical trifoliate) pedicellarise (Rev. p. 666, 

 PI. XXVI. 24) are evidently small tridentate pedicellariae and cannot be said to be (.characteristic of 

 the Spatangoids propers. 



The spicules of the tubefeet have been described and figured by Perrier; it may only be 

 mentioned here that no spicules are found in the transformed tubefeet (gills) of the paired abactinal 

 ambulacra — as upon the whole spicules are generally wanting in these tubefeet in the irregular 

 Echini. As for the structure of the penicillate tubefeet round the mouth I may refer to the very 

 beautiful researches of Loven. The intestine and genital organs do not contain spicules in their walls. 



A young specimen of this species, ca. i2 mm in length, has been figured and described by 

 Agassiz (Revision of Ech. p. 331. PI. XL f. Figs. 19 — 22), and further Loven has given very impor- 

 tant information especially of the development of the apical system (On Pourtalesia. p. 74, 77. PL XVIII. 

 Figs. 209— 219); the smallest specimen examined by Loven was 5 - 4 mm in length. From the St. 86 of 

 the «Ingolf> there are some small specimens, the youngest only 4 mm in length, which enable me to 

 give some additional information of the changes during growth in this species. 



The specimen of 4""" length (PL XVI. Fig. 29, 31, 34) differs very considerably in outline, espe- 

 cially in side view, from the grown specimens. The anal system is on the abactinal side, rather near 

 the vertex; the actinal plastron forms a rather prominent hood, the point of which is surrounded by 

 the fasciole, which is, in the spine-covered specimen, very conspicuous. Only one ambulacral plate 

 the 6th, 1 reaches w T ithin the fasciole; the 7th is just traversed by the fasciole. No pores are accordingly 

 as yet developed within the fasciole (PL XVI. Fig. 24). The actinostome is as yet almost quite embry- 

 onal, the labrum only just beginning to widen anteriorly. The abactinal ambulacra are very simple; 



1 In this specimen it is abnormally the 5th plate in Ambulacrum I. a, which reaches within the fasciole. In V. b it 

 is the 6th, as is the normal case. 



