SPOiNGES.-HALLMANN. ,,- 



that in P. clopetaria, Schmidt, i with its "pegtop-shaped" styH 

 we have a species in which there are present two kinds of prin- 

 cipal and two kinds of accessory spicules. The differentiation 

 of the auxiliary megascleres into two groups, as in Rhaphi- 

 dophhis, appears to have occurred but seldom. 



An interesting point in connection with the microscleres, 

 and one which possesses considerable classificatory importance 

 is the rarity of the occurrence of sigmata and toxa in the same 

 species, 'i hese two microscleres are found together in certain 

 Mycalina% but not to my knowledge in any species of the Myx- 

 illinae. P\irthermore, in the latter sub-family, the microscleres 

 which occur in association with toxa are (except in Ploca- 

 miopsis) isochelaj palmata;, whilst those associated with sig- 

 mata are isochelae arcuatae, isancorte, or rhaphides (usually in 

 dragmata). Thus we have on the one hand the genera 

 Hymeraphia, Microciona, Clathria, Rhaphidolphiis, Ophlita- 

 spongia, Echinoclathria, Heteroclathria, Plocamia, Acarnns, 

 Microtylotella, Fusifer, Cornulum, and Artemisina in which 

 the microscleres are toxa and (or) isochelse palmata; but not 

 sigmata ; and, on the other hand, Leptosia, Stylostichon, 

 Ectyodoryx, [Jssodendoryx, Clathrissa, Crella, Grayella, 

 Paramyxilla, Forcepia, Leptobasis, Hamigera, Dendoricella, 

 Histodeniiella, Histodenna, Hymeuaticora, Myxilla, Ectyo- 

 niyxilla and Melonanchura in which the microscleres are 

 sigmata and isochela? arculata; or isancorse with or without 

 trichodragmata, but not toxa. There can scarcely be any 

 doubt that these groups of genera are representative of two 

 distinct lines of evolution in the Myxillinae ; and since they 

 comprise between them the majority of the species the ques- 

 tion naturally arises as to whether they can be utilised as a 

 basis for the division of the sub-family. The probability is 

 that they can. In the former group, the accessory megascleres, 

 when present, are well distinguished from the principal, and 

 the auxiliary spicules are typically stylote ; whereas in the 

 latter, principal and accessory spicules as a rule are not widely 

 different in form, and often graduate insensibly one into the 

 other, and the auxiliary spicules are topically more or less 

 diactinal. This is not only significant in itself, but it provides 

 a means whereby one is enabled to arrive at an opinion con- 

 cerning the allotment of most of the remaining genera. Thus 

 the genera Raspailia and Claihriodendrou (and with them Sy- 

 ringcUa) ; Echinodictyuni, Trikcntrion and Cyanion; Aido- 

 spotigus ; and Spanioplon — all of which are lacking in micro- 

 scleres — are evidently to be assigned to the former group ; 

 Acheliderma, Tedania and Dragmatyle ; Hymetyochota, loiro- 

 chota and AtnphiastrcUa ; and perhaps also the somewhat aber- 

 rant lophon and PociUon — to the latter. To the former group 



1 Kidley— Jour. Linn. Soc, Zool., xv., 1881, p. 479. 



