88 SVEN LOVEN, ON THE ECHINOIDEA DESCRIBED BY LINN.EUS. 



tbat when the animal has attained a diameter of 5 ram., Tah. 

 9, jig. 5, a succession of plates devoid of tubercles has built 

 up the dorsal portion of the flattened test and expanded it to 

 such a degree that the oldest plates, the bearers of the first 

 spines and tubercles, have nearly all been made to move över 

 upon its ventral side, under the equator. There the tubercles, 

 already large and crowdinp;, leave little room for the epistroma 

 to develope, while this at the same time has for itself alone 

 the whole of the dorsal side. 



The periproct, Tah. 8, jig. i, presents a sub-oval, rounded 

 outline and is already slightly drawn backward into the co- 

 stals 1 and 5. Its long diameter, to which the short one is 

 at right angles, lies, exactly as in the fullgrown animal, 

 between a point a very little in front of the suture between 

 the costals 3 and 4, and another, opposite, a little behind the 

 middle of the costal 1. It is already provided with the nor- 

 mal four closing valves. There is no indication of sexual 

 pores. The costal 2, somewhat larger than any of the other 

 four, is penetrated by a few madreporic pores. 



The periproct is circumscribed by a very couspicuous 

 and regular pentagon, formed by the epistroma, fig. i, of five 

 straiirht linear sides that cross the sutures between the costals, 

 while its angles, entering upon these, come to be placed on 

 their middle line, at some distance from the periproctal mar- 

 gin. This pentagon, accordingly, is heterotropous to the pri- 

 mitive pentagonal central ossicle of the calyx, already converted, 

 in consequence of the eruption of the excretor}^ opening, into 

 the secondary structure of the rounded proctal apparatus. 

 Inside the pentagon, on that inner portion of each costal 

 which has been modified in connexion with this remodelling, 

 the short and steep slope towards the periproctal margin is 

 no more what it was at au earlier age, but paved, like the 

 valves, with crowded, minute, lengthened nodules, in rows di- 

 rected downward. Each side of this inner pentagon is a 

 ridge formed by the rising of the epistroma, and consists 

 of a seemingly cellulous tissue supporting a nearly regular 

 row of glossy transparent globules. Each of its angles closely 

 approximates the base of a high protuberance, a sub-pedun- 

 culated, conical, berry-like, regular compaction of numerous 

 minute oval globules, fig. 3. From the base of this protube- 

 rance there extend, on each side, other ridges, smooth and 



