126 ECHINOIDEA. II. 



Agassiz (Rev. p. 666) rightly refers thi.s form to the tridentate form, thongh I might not strictly call 

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

 foUows Per ri er in regarding them as ophicephalous pedicellariæ. 



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

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

 aniong the small abactinal spines in larger specimens; they are fonnd only on the abactinal side and 

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

 articular snrface, 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- 

 plnsis 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 pedicellariæ (PI. XVI. Figs. 2, 22) are very snuill and delicate (the head ca. 014'"™ 

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

 lower corners are rather sliarp; 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 pedicellariæ has first 

 been seen by Koehler; what Agassiz mentions as ^typical trifoliate pedicellariæ (Rev. p. 666, 

 PI. XXVI. 24) are evideutly small tridentate pedicellariæ and cannot be said to be v characteristic of 

 the Spatangoids propert. 



The spicules of the tubefeet have been described and fignred by Per rier; 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 wantiug in these tubefeet in the irregular 

 Echini. As for the structure of the penicillate tubefeet round the moutli 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. 12""' in length, has been figured and described by 

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

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

 Figs. 209— 219); the smallest specimen examined by Loven was 5'4'"'" in length. From the vSt. 86 of 

 the « Ingolf :> there are some small specimens, the youngest only 4'"'" in length, which euable 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,' reaches within the fasciole; the 7tli is just traversed by the fasciole. No pores are accordingly 

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

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



• In this specimeu it is abnormali)' the 5th plate in Ambulacrum I. a, which reaches within the fasciole. In V. b it 

 is the 6th, as is the normal case. 



