46 S. LOVEN, ON POURTALESIA, A GENUS OF ECHINOIDEA. 



same aberrant structure. It will be seen further on, that this structure is peculiar to 

 the subanal pedicels, and it may be that in the cases here mentioned it is assumed 

 by the aborally most distant among the phyllodean pedicels. 



The mode of development and the growth of the phyllodean pedicels may be seen, 

 partially at least, in very young specimens. In the young Abatus cavernosus, still 

 astoraous and aproctic, PL XIV, fig. 163, there are five in the ambulacra I and V, two 

 of which are in the \ a 1 and two in V b 1, one in each oi I b 1, 2, 3, and of V, 

 a 1, 2, 3; in II and IV: two in a, 1, one in a 2, and one in each of b 1, 2, 3; in III: 

 two in b 1, one in b 2, and one in each of a 1, 2, 3. They are all simple, rounded, 

 elevated knobs. The young of Echinocardium flavescens O. F. M., PL XV, fig. 172. 

 measuring only 1,7 millimeter without the spines, having the pentagonal peristome 

 placed only a little before the middle, with the newly-formed oesophageal opening in 

 its very centre, and presenting the five first spherids, one in each of the uniporous 

 plates 1, ^) has fifteen phyllodean pedicels: two in each of the bi-porous plates, one on 

 each of the uni-porous. The following plates are also provided with pores, but the 

 pedicels beginning to form over them could not be discerned, probably from their too 

 great transparency. Each of tlie fifteen pedicels presents a short tubular shaft, and a 

 simple, tumid, semi-globular head, in the centre of which is seen a roundish, convex 

 lamina of calcified reticular tissue, fig. 176. In a specimen only a trifle larger, l,'.t mm., 

 fig. 175, the head of the pedicel of one of the uniporous plates, V a, fig. 177, has 

 become ovate, and two circular wheels have begun to form on its centre-piece, one of 

 them directed against the small end of the head, the other, smaller, nearly opposite, 

 and on their outer sides the calcified fibres are seen to interlace and protrude. In 

 the pedicel of V, fig. 175, 178, two rounded lobes have grown out, and to each of them 

 there is a corresponding wheel, on the point, as it appears, of coming off the central 

 network, and out of its fibres the rod is seen to rise outwardly. Similar changes are 

 seen in the young specimen of Abatus cavernosus, in which the oesophageal opening 

 is just on the point of forming. ") In another specimen of Echinocardium flavescens, 

 of 3 mm., fig. 174, which has the oesophageal opening moved a little behind the centre 

 of the pentagon, the second pair of plates, in each of the paired ambulacra, presents 

 their newlj^-formed pedicels. The disk of the older pedicels has now expanded into 

 two or three lobes, fig. 179, 180, each containing a wheel, free from the central net- 

 work, and with a lengthened rod. Underneath are seen the long, arcuated, spinj^, 

 transverse spicules of the ring. The central network seems not so large, relatively to 

 the expansion of the disk, as it was at first; in adult specimens it is absent, as 

 generally among the Spatangidaj, a store used up by the growing rods. A specimen 

 of 5,3 millimeters has disks, fig. 181, with eight clavate filaments, forming a marginal 

 circle, and one that seems to begin another, inner circle. Their number appears to 

 increase rapidly; a Spatangus purpureus of 14 millimeters already presents the same 

 number as one of 51 millimeters. 



1) Etudes, p. 36, pi. Ill, fig. 33—3.5. 

 -) See •n'oodcut p. 26. 



