22 K. LdVEN, ON J'((URTALK8IA, A GENUS OF ECIIINOIDKA. 



the backward grovvtli of the abdomen, combined with tlie tendency of the alimentary 

 canal towards an anter()-])osterior direction, its excretory end, after having opened — 

 which, as far as I liave been able to observe, is done simultaneously with the o]>enin<>; of 

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

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

 distance from the calyx. A Aoung specimen of Echinocardium flavescens O. F. M., 

 1,7 mm. in length, PL XV, fig. 173, has the opened periproct 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 lamime of the anal membrane are disposed in two 

 rings, surrounding five converging triangular scales. Thus here also the stonuito- 

 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 Jett'reysi it is placed as far back perhaps as 

 in any other species of the Neonoraous forms, PL I, Jig. 3, 4; II, 0; 111, 13, over the 

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

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

 terradial plates 7, 8, 9 oi b a and h, tliat form, Avith 5 and 6, the circum-anal 

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

 and V h, 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 laminae; it is the site of 

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

 has larger scales. This structure agrees with Avhat is seen in the Cassidulidte. In this 

 group the periproct, transverse and reniform, is likewise placed in a depression above 

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

 tilling 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 Spatangidtc, 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 lamina?, as in the 

 young of Echinocardium flavescens described above, PL XV, fig. 173, or in Palajostoma 

 mirabile Gray, PL XVI, fg. 184, 186, IHI '). 



In Pourtalesia Jeflf'reysi and its congeners only one fasciola is present, a well- 

 marked subanal fasciola encircling the caudal prolongation, PL 1, jig. 1, 2, 3 ; 11, 9. 

 Like the corresponding fasciola of the Spatangidas, 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 h, 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, fig. 38, it has the same position, which it probably 



1) Etudes, pi. XIII, iig. 113, 118; XXIX, 190; XXX, 193; XXXI, 196; XXXII, 199; XXXIV, 204; 

 XXXV, 207; XXXVl, 212; XXXVll, 217; XXXVIII, 221; XXXIX, 226; XLII, 231; XLIII, 234. 



