106 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.81 



The chelas are quite commonplace, of the Microoiona sort, and very 

 abundant. The toxas are also often abundant and exhibit a most 

 amazing variation in size, at least 40/x to 340)it, with all sizes in be- 

 tween of approximately equal abundance. 



The so-termed dermal tylotes are more properly secondary or 

 tangential connections between the ascending columns near the sur- 

 face of the sponge. Their terminal spines, often just four in num- 

 ber, are nearly '2ix long but so very fine that they can not be clearly 

 seen without oil immersion. Deeper in the sponge their place seems 

 to be taken by the cladotylotes, which are only fastened at one 

 end, so that they are also quite properly to be termed echinating 

 spicules. In this species they are remarkable for their tetrasym- 

 metrical plan, so that they become hexactinal spicules, superficially 

 resembling the clavules of the proper hexactinellid sponges. The 

 embedded end (encased in spongin) shows four hemispherical pro- 

 trusions matching the four clads at the other end. Besides the 

 larger, smooth-shafted " palm trees " (fig. 63, C) there are small 

 curve-spined "rose stems" (fig. 63, F). Intermediates in size, with 

 but a few spines, occur (fig. 63, E) , but are rare. 



Heated cladotylotes when studied with oil immersion do not show 

 connection between the axial canals of the clads and that of the 

 rhabd. Those of Acmmus ternatu^ have usually three clads, and 

 were used by Dendy and Ridley (1886, p. 157) as a chief argument 

 for the theory that monaxons were closely related to the tetraxons, 

 but in tetraxon spicules (such as anatriaenes) the clads have their 

 axial canals connected to that of the rhabd. In Acarnus these 

 spicules seem to have been first tylote, with the clads added later. 

 This is completely homologous with the ends of the rays of hexac- 

 tinellid discohexasters (see Lendenfeld, 1915, pi. 9) and the ends of 

 hexactinellid amphidisks (see Kirkpatrick, 1910). There is further 

 homology between the hexactinellid amphidisks and those of such 

 monaxonid genera as lotrochota and Ephydaiia. Monaxonid chelas 

 are merely amphidisks with the central shaft displaced laterally 

 until it has coalesced with teeth with which it has made contact. 

 Spicules very strongly suggestive of hexactinellid relationship are 

 to be found in such diverse monaxonid genera as Acarnus, Axos, 

 Cliothoosa, DoUchantha^ Endectyon^ Proteleia, Hymeraphia^ and 

 Raspailia. Undoubtedly many seemingly monaxonid sponges, such 

 as the epipolasids, are really reduced tetraxonids, but the majority 

 are rather closer to the hexactinellids. Separate orders are indicated 

 from monaxons and triaxons, but Dendy's Astrotetraxonida and 

 Sigmatotetraxonida imply relationships not borne out by the 

 evidence. 



