84 S. LOVEN, ON I'OUKTALESIA, A GENUS OF ECIIINOIDEA. 



is fully inaiiitaiiied in one sprcics only, Pourtalesia cariiiata, but discarded in P. Jeflf- 

 reysi, P. layuucula, P. ci'iatopyga and Echinucrupis cuneata, in Avliicli tlie first jjlatc 

 of the III, uni-porous in <i, M-porous in b, alone presents a remnant of the other- 

 wise universal formula, wliile the first plates of the paii'ed amljulacra 11 and IV, I and 

 V, are all synimeti'ieal on either side of the mesial line, tlius conforming to the grow- 

 ing tendency towards u strict bilaterality, and a graduall}' more decided contrast be- 

 tween the ventral side and the dorsal. 



Tlie posterior interradium, 5, is dismembered in Pourtalesia Jeffreysi, P. lagun- 

 cula and Spatagocystis. Ventrally the / 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 sternum, hi P. cari- 

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

 guous to the stermini. In P. Jeffreysi the labrum is very minute, in the i-est of species 

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

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

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

 b a 3, b b :j, the pre-anals 5 a 4 — 6, 5 b 4 — 6', the expanded periproctal series, .') a 

 7 — 9, 5 b 7 — 'J, and by the dorsal sequence of [)lates gradually narrowing, and in P. 

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

 calycinal system, but by means 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 Echinoerepis 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 beyond tlu' ambulacra II and IV, and the costal 4 even occasionally severed 

 from the system by detached plates of the fifth 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 Echinoneida3 — among the whole of the Neonomous Echi- 

 iioids, the Pourtalesiada) are honioiopodous. The pedicels, all ambulacral, are uniform, 

 sim])Ie, not disciferous, none of them formed into brancliial 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 restricted part of the sub-labial region, on the first plates 

 of the ambulacra I, II, W , V, and absent on the frontal. Ill, — a characteristic without 

 parallel. 



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

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



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

 all rather slender, not crowded, except on the sternum and on the palate of the buccal 

 cavity. 



