KONGI,. SV. VET. AKAlMiMlENS HANIJL. BAND. 19. N:0 7. 59 



v 



Palfcostoma mirabile, fig. 139, presents deeply suiik phyllodean peinpodia, with the 

 two perforatioiis not separated, but unitcd by an open slit. The speciinen examined 

 is, however, young and still retains this juvenile cbaracter, the poi'e being at first 

 simple, not geminous. ^) 



When the entire series of Adete, Prymnadete and Prymnodesmian Spatangidae 

 is viewed as a whole, the cornmon characters of tlieir phyllodean peripodia is apparent: 

 their general form, their great size relatively to that of the other peripodia bearing 

 tubular pedicels, the parallel direction of the two peripodia of the biporoiis plates, 

 the gradually prevailing abortion of their aboral perforation. The similarity is in 

 fact such as to justify the conclusion that the principal characteristic of the modern 

 SpatangidaB, the penicillate phyllodean pedicels, was present already in the earliest 

 Adete forms, in Collyrites, Holaster, Anancites, Hemipneustes, Cardiaster. 



Where the penicillate pedicels are succeeded by the much smaller simple pedi- 

 cels, the peripodia, again with geminous perforations, at once become very minute. 

 In the Meridosternal Adetes, as in Collyrites, Anancites, Hemipneustes, they con- 

 tinue so in the five ambulacra all up to the petala, in Holaster and Cardiaster 

 through the middle part of the front ambulacrum, and in the four paired ambulacra, 

 I and V, H and IV, up to their petala, thus suggesting the probable absence, in these 

 old types, of peculiar subanal pedicels. These appear in the Amphisternal Spatangidaj 

 in I a and V h, supported by peripodia always larger than the corresponding in I h 

 and V a, though in a various degree. Already in Echinopatagus, Hemiaster, and in 

 Palasostoma, that of V 6 surpasses that of V a, and in the great majority of recent 

 forms, Prymnadete as Prymnodesmian, the difference is more or less marked, jig. 140 

 — 148. But, as far as my present knoAvledge extends, the structural differences of the 

 subanal pedicel, penicillate, semi-penicillate, or simple and devoid of filaments, are 

 not distinctly associated with corresponding diversities in the peripodium. The peni- 

 cillate subanal of Echinocardium is supported by a peripodium not very unlike that 

 of the simple pedicel of Meoma, and the similarities or dissimilarities between the sub- 

 anal peripodia of different genera appear to bear no very close relations to the resem- 

 blances or diversities between their pedicels. The like seems not far from being 

 the case with those of the front ambulacrum. There is some resemblance between 

 those of Hemiaster, jig. 138, and of Schizaster, /i^. 140, — they are lengthened, narrow, 

 and bridged över by a convex protuberance, — and that of Palasostoma, jig. 139, is 

 not very different — , and these three genera have frontal pedicels with large radia- 

 ting lamels in the disk; but the nearly similar frontal pedicels of Brissopsis, jig. 143, 

 have very diiferent peripodia, Those of the simple frontals in Spatangus, Maretia, 

 Lovenia and Meoma are minute, those of the more complicated, as in Agassizia and 

 others, are much larger. 



In the greater number of Neonomous forms, Cassiduline and Spatangean, the 

 pedicels of the dorsal portions of the ambulacra are transformed into but slightly 

 extensible, generally triangulär branchial leaflets. These portions of the ambulacra, 



1) Études, pl. XVII, fig. 151. 



