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



A clue attention paid to the developiuent of parts during the growth of the indivi- 

 dual aniiual has more tlian once veconciled discrepancies as great as that of the cal}'- 

 cinal system in the Ethmophracti atid the Ethinolysii, the Mesozoic type and the Cenozoic. 



In the young of Abatus cavernosus, Pl. XIV, jig. 164, 164 A, the calycinal sy- 

 stern, relatively large, presents five radials I, II, III, IV, V, each bearing a tentacle, 

 and four costals, 1, 2, 3, 4, araong which the 2 lias becorae already the site 

 of the madreporite. The central and open part is overlaid, within the general enve- 

 lope, by a membrane in which are seen detached niinute calcified lamina?, pi'esuinably 

 radiments of the central ossicle and the costal 5, nowhere extant among the Ethmo- 

 phracti, but here to be developed, Pl. XVIII, fi.g. 220, after the backward passage of 

 the excretory end of the aliraentary tube. 



Young Spatangi, with the raouth and the vent opened, and living free on the 

 bottom of the sea, very early present a calycinal system completed by the presence of 

 the centi'al disk and the costal 5. Different stages of Echinocardium flavescens O. F. 

 Muller, Spatangus purpureus O. F. M., and Brissopsis lyrifera Forbes, Pl. XVII, XVIII, 

 XIX, may serve as examples showing the development of the calycinal system and 

 the movement of the madreporic apparatus in the Spatangidaa Ethmolysii. Of the tirst- 

 named the calycinal system is represented Pl. XVII, jig. 197 — 207, as it appears in 

 speciniens of different dimensions, from mm. o,r) : 3 to mm. 36 : 32. In the youngest 

 the five radials are present with their ocular pores. The whole system, up to the in- 

 dividual size of mm. 30 : 26, is more or less distinctly pentagonal. The central ossicle 

 together with costals 2, 3, 5 are united into one continuous middle area, extending 

 throuo-h the whole leno-th of the system, with the radial III in front, the ra- 

 dials IV and V and costal 4 on the left, and radials I and II together with costal 1 

 on the right. At first, fi.g. 197 , 198, the madreporite is a single pore placed nearly in 

 front, then there are two or three pores, ^(7. 199 — 205, of which the last added is more 

 towards the middle; in a specimen of mm. 14,5: 12, Jig. 205, out of five pores two 

 are posterior. Meanwhile the costals, at the total size of mm. 10, : 9 and mm. 12 : 10, 

 jig. 203, 204, have been provided with sexual pores, at first so rainute as easily to be 

 taken for madreporic pores, but becoming larger according as the reproductive organs 

 are developed. At mm. 30 : 26, jig. 206, the swarm of madreporic pores lies more 

 than half behind the middle, and at mm. 36 : 32, jig. 207, nearly the whole of it be- 

 hind the costals 1 and 4, and the costal 5 has been driven backward into the inter- 

 radium 5; but still its intact margin is seen to limit the pressure of the pores. And 

 during this transference, in this species as in those next to be described, the middle 

 part, expanded as long as occupied by the growing madreporite, contracts again when 

 it has passed, yielding to the pressure exerted by the interradia. 



A series of young stages of Spatangus purpureus O. F. M., from mm. 5 : 4 to mm. 

 24 : 21, presents similar modifications, Pl. XVIII, jig. 209 — 219. There is the same 

 drawing together of the sexual openings and narrowing of the middle area, after the 

 recession of the madreporic filter, which is richer in pores than that of Echinocardium, 

 and much more expansive, so much so as largely to invade, at mm. 53 : 50, the costals 

 1 and 4, to fill to the ver}' brim the costal 5, stretching it to the utmost and leaving no 



