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



is fiilly nuiiiitiiiiicd iii uin' spccics uiily, Pourtalesia carinata, but discardod in 1*. Jeff- 

 reysi, F. lagiincula, P. ccratopyga and Echinocrcpis cuiieata, in wliich tlie tirst plate 

 of tbe JIl, Luii-[)Oi'ous in a, bi-porous in b, alone presents a rcmnant of the otlier- 

 wise universal formula, while the Hrst plates of the paired anibulacra II and IV, I and 

 V, are all syuunetrical on either side of the mesial line, thus conforraing tothegrovv- 

 ing tendency towards a strict bilaterality, and a gradually more deeidcd eontrast be- 

 tween the ventral side and tlie dorsal. 



The posterior interradium, 5, is dismenibered in Pourtalesia Jetfreysi, P. lagun- 

 cula and Spatagocystis. Ventrally the i of I and V, the / of 1 and 4, and the 2 of 

 I and V, are interposed between 5, 1, the labrum, and 5, 2, the sternuni. In P. cari- 

 nata, perhaps also in P. ceratopyga and in Echinocrepis cuneata, the labrum is conti- 

 guous to the sternuin. In P. Jeffreysi the labrum is very minute, in the rest of species 

 observed large and expanding aborally. The sternuin is all of one piece in P. Jeffreysi, 

 the plates a 2 and 6 2 having coalesced, while in P. carinata they appear to be se- 

 parate. It is followed in P. Jeffreysi by the regular double Spatangean episternum, 

 5 a 3, 5 b 3, the pre-anals 5 a 4 — 6, 5 6 4 — 6, the expanded periproctal series, 5 a 

 7 — O, 5 b 7 — .'/, and by the dorsal sequence of plates gradually narrowing, and in P. 

 Jeffreysi, P. laguncula, P. earinata, P. ceratopyga, and Spatagocystis, reaching the 

 calycinal system, but by ineans of detached pairs of plates only, enclaves between the 

 1 and 4, where these close mesially, thus distantly recalling Collyrites. 



The calycinal system, somewhat Spatangean in Echinocrepis by the radials I and 

 V being distinct, contiguous and closing, and the sexual pore of the costal 2 abortive, 

 in the other species, at least in Pourtalesia Jeffreysi, P. laguncula, P. ceratopyga, is 

 subject to a degree of degeneration seen nowhere else. Its outline is irregular, the 

 sutures obliterated to an extent unknown elsewhere, the radials have disappeared, and, 

 while there is no trace of a restored costal 5, the 1 and 4 are displaced forward 

 nearly beyoncl the anibulacra II and IV, and the costal 4 even occasionally severed 

 from the system by detached plates of the lifth interradium; and while thus the struc- 

 tural consistency of the system is giving way, its relative size is reduced, and it is 

 drawn forward and widely removed from the bivious ambulacra. 



Alone — with the Echinoneida^ — among the whole of the Neonomous Echi- 

 rioids, the Pourtalesiadas are homoiopodous. The pedicels, all ambulacral, are uniform, 

 simple, not disciferous, none of them formed into branchial leaflets, the sub-oral 

 and upper frontal pedicels larger than the rest, which are very minute. 



The spherids are uncovered, more various in number than usual, but always 

 stationed exclusively on a restiicted part of the sub-labial region, on the first plates 

 of the ambulacra I, II, IV, V, and absent on the frontal, III, — a cliaracteristic Avithout 

 parallel. 



The single fasciola present is sub-anal, but holds not the same relation to the 

 plates of the bivium, as in the Prymnodesmic Spatangidte. In one species it aborts. 



The spines are Spatangean, partly curved and oar-like, partly almost straight, 

 all rather slender, not cfowded, except on the sternum and on the palate ofthebuccal 

 cavity. 



