BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 13. AFD. IV. N:0 5. 129 



grown specimens, wliicli always liave thc dorsal pores disposed 

 l)v triads, in sliohtlv ciirved lono;itudiual arclies that on the 

 vcQtral sido become diagonal. But the specimen from Avliich 

 LiNN.EUS described his E. saxatilis was assuredly not fuUgrown. 

 Hc says: »magnitudo minor-, and refers to Rumphius, t. XIV, 

 f. A., in 1752 to that ligure alone, chiefiy, it may be pre- 

 sumed, with regard to its size, 27 mm. in diameter. Thus 

 the E. saxatilis L. oiight to bo looked for in the young of 

 some species of the groiip. Its diagnosis exchides the genus 

 Echinothrix, Astropyga deviates by its general form and the 

 numerous series of its interradial primary verrucae, as does 

 Centrostephanus by their whole disposition, and Ave are led 

 to the genus Diadema ( Ikay and to its long-known species of 

 world-wide inter-tropical distribution, the D. setosum Gkay. 



If the diagnosis and description of the E. saxatilis are 

 tried on a ^^oung specimen of the Diadema setosum Gkay, 

 25 mm. in diameter, the result will be as follows. 



The general form, »figura», is hemisphserical and round, 

 und more depressed than that of the E. Diadema. Of the 

 general form the term »deprcssus» is used thrice in the whole 

 of the Echinoids: for these two Diadematidte, and for the E. 

 Cidaris. If it is understood to mean liattened, its combination 

 witli /hemispha^n-icus and »globosus» would iuvolve a contra- 

 diction, but it must be strictly taken in the sense given to it 

 in the Philosophia Botanica'). Thus understood it is clearly 

 seen speciallv to refer to the region of the >centrum>:^, Avhich 

 in the Cidarida^ is more or less flattened, and in the Diadema- 

 tida^ almost characteristically sunk, and noAvhere more so than 

 in tlie Diadema setosum Gkay. 



The periproct comparcd with that of the E. Diadema is 

 large: *foramine magno». Its long diameter, I — 3, is 0,:->s of 

 that of the calyx, 0,i4 of that of the test. The corresponding 

 measures in tlie E. Diadema are O,.") 16 and 0,1:26. 



The ambulacra, that is the zon» poriferse are ten in num- 

 ber, placed tAA'o and tAA'o close together, their AA'ell-knoAA-n dis- 

 position in the Diadema setosum Gkay. The expression: !>pa- 

 ribus approximatis» is used also of Arbacia Lixula, and the 

 narrow ambulacra, in particular tli(> disposition of the zonte 

 in that species so much resemble the same parts in the young 

 Diadema saxatile, that the fioure A on the V\. XIV in KuM- 

 ') See above p. SS. 



