22 S. LOVEN, ON POURTALESIA, A GENUS OV ECIIINOIDEA. 



the backward growth of the abdomeii, coiiibined Avith thc tciidency of the aliiiiciitary 

 canal towards an antero-posterior direction, its excretory end, after havirig opened — 

 whicli, as far as I have been able to observe, is done simultaneously with the openiiig of 

 the oesophageal end — is drawn back towards the plates of the sixth pair, and that 

 subsequently the seventh and following subanal plates are added, increasing its 

 distance from the calyx. A young specimen of Echinocardiuni flavescens O. F. M., 

 1,7 min. in length, Pl. XV, Jig. 173, has the opened pei"iproct high up on the back, 

 near the calyx, from which it is separated by only two interradial plates. It is large, 

 widely elliptic, and the calcified lamimi', of the anal membrane are disposed in two 

 rings, surrouuding tive converging triangulär scales. Thus here also the stomato- 

 proctic axis is not very far from vertical. 



The manner in which the periproct is formed in Pourtalesia will probably never 

 be known. In the adult of Pourtalesia Jeffreysi it is placed as far back perhaps as 

 in any other species of the Neonomous forms, Pl. I, jig. 3, 4; II, 9; 111, 13, över the 

 caudal prolongation, in the deep depression between the interradials 5 a and b, 5 to 

 O, and the ambulacrals I a and V 6, 5 to 7. It is transverse, cut out in the in- 

 terradial plates 7, 8, 9 of 5 a and b, that form, with 5 and 6', thc circum-anal 

 region, which is expanded and received on either side into the sinus made by I a 

 and V b, plates 5-7. The anal membrane is divided into two portions, an upper 

 and overhanging one, between the interradials 8 and 9, and an under and rising one, 

 between 8 and 7. The upper is broader and covered with smaller lamina?; it is the site of 

 the excretory opening, a narroAv transverse slit; the under portion, semi-circular, 

 has larger scales. This structure agrees with what is seen in the Cassidulida3. In this 

 group the periproct, ti'ansverse and reniform, is likewise placed in a depression above 

 the slight caudal prolongation, and the posterior under portion of the anal membrane, 

 lilling nearly the whole, is covered with a few large scales, while the upper, with the 

 transverse excretory opening, is very small and drawn up close under the margin of 

 the somewhat projecting post-anal plates. In the Spatangidaa, on the other hand, the 

 membrane is of one piece, with its scales arranged concentrically all around, and the 

 excretory opening, roundish and sub-central, closed by converging laminaa, as in the 

 young of Echinocardiuni flavescens described above, PL XV, fig. 173, or in Palaiostoma 

 mirabile Gray, PL XVI, Jig. 184, 186, 191 '). 



In Pourtalesia Jeffreysi and its congeners only one fasciola is present, a well- 

 marked subanal fasciola encircling the caudal prolongation, PL 1, jig. 1, 2, 3 ; II, 9. 

 Like the corresponding fasciola of the Spatangidte, it crosses the third and the fifth 

 plate of the interradium 5, but, contrary to what is the universal rule in that group, 

 it traverses, not the sixth and certain following plates of the rows I a and V b, but 

 the fourth plate alone, which by itself fills the episternal angle. It thus marks off, 

 not the fifth, but the third plate of both rows as the hindmost of the ventrals. In 

 Pourtalesia laguncula, PL VI, jig. 38, it has the same position, which it probably 



1) Études, pl. XIII, %. 113, 118; XXIX, 190; XXX, 193; XXXI, 196; XXXII, 199; XXXIV, 204; 

 XXXV, 207; XXXVI, 212; XXXVII, 217; XXXVIII, 221; XXXIX, 226; XLII, 231; XLIII, 234. 



