KONGL. KV. VET. AKADKMIENS IIANDL. BAND. 19. N:0 7. 59 



Palifostorna mirabile, fLCf. 139, presents deeply sunk ])hyllodean peripodia, witli the 

 two perforations not separated, but united by an o])en slit. Tlie specimen examined 

 is, however, young and still retains this juvenile character, the pore being at first 

 simple, not geminous. ^) 



When the entire series of Adete, Prymnadete and Prymnodesniian Spatangidac 

 is viewed as a whole, the common characters of their 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 peri})0(lia of the biporous plates, 

 the gradually prevailing abortion of their aboral perforation. The similai'ity is in 

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

 Spatangida3, the penicillate ])hyllodean pedicels, was present already in the earliest 

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



Where the penicillate pedicels are succeeded l)y the much smaller simple ])edi- 

 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 and)ulacra 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, II and IV, up to their petala, thus suggesting the probable absence, in these 

 old types, of peculiar subanal pedicels. These appear in tlie Amphisternal Spatangidte 

 in I a and V 6, supported by peripodia always larger than the corresponding in 1 b 

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

 Palajostoma, that of V b surpasses tliat of V a, and in tlie great majority of recent 

 forms, Prymnadete as l^rymnodesmian, the difference is more or less marked, jiy. 140 

 — 148. But, as far as my present knowledge 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 tliat 

 of the simple pedicel of Meoma, and the similarities or dissinularities 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. VJ8, and of Schizaster, /;//• I4i), — they are lengthened, narrow, 

 and bridged over by a convex protuberance, — and that of Pala^ostoma, fig. 139, is 

 not very different — , and these three genera ha\e frontal pedicels with large radia- 

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

 have very different 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 luunbin- of Neonomous foi-ms, Cassi<luline and Spatangean, the 

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

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



') Etudes, pi. XV 11, li-. 1.51. 



