Ixvi THE VOYAGE OF H.M.S. CHALLENGEE. 



of the hooks. So far as we know certainly, the diancistra do not occur amongst the 

 Desmacidonidse. Schmidt, however, describes^ a sponge under the name Vomerula 

 tibicen, which is stated by him to contain " Doppelankern " and " Pflugscharspangen ; " 

 unfortunately there are no figures, and the entire description is comprised in the fol- 

 lowing words : — " Vomerula tibicen. Neu — Vom Habitus des Desmacidon tunicatum, also 

 incrustirend, mit Oberhaut, welche in ^ bis 1 Cmtr. lange Rohren iibergeht. Nach den 

 Kieseltheilen ware diese Art ein Desmacidon zu nenuen, das ausser den characteristischen 

 Korpern, nJimlich den etwas gebogenen Nadeln, den Doppelankern van 0'0257 Mmtr., 

 und den etwa halb so langen Spangen, auch noch die grossen Pflugscharspangen von 

 0-157 Mmtr. enthiilt. 



" Es ist damit eine abermalige Combination und Uebergangsform verwirklicht. Ob 

 wir es mit einer constanten Form oder mit einer individuellen Abschweifung von 

 Vomerula zu Desmacidon oder umgekehrt zu thun haben, ist nicht zu entscheiden. — 

 Fundort : Grenada, 170 Faden." 



The combination of spicules here indicated would be so unusual were the " Pflug- 

 scharspangen " true diancistra, that we cannot help feeling some doubt on this point, and 

 thinking that possibly they may be only large contort sigmata like those of E&perella 

 simonis, nobis, and somewhat resembling the true diancistra ; or, supposing that they 

 are true diancistra, then perhaps the chelae occur as foreign bodies, as in the analogous 

 case of Sceptrella regalis {vide supra). Further information concerning this point is much 

 needed ; if diancistra are really present, and also chelje, then the species in question 

 forms a most important link between the subfamilies Hamacanthinse and Esperellinse ; 

 it would, of course, be referable to the latter. 



The subfamily Hamacanthinse is divided into two genera, according to whether the 

 megasclera are diactinal (as in Hamacantha) or monactinal (as in Vomei^la). 



The DesmacidonidfB, constituting our third family, are characterised by the presence 

 of chelate microsclcra. These spicules are, unlike the sigmata, of such very complex and 

 remarkable form that we cannot believe them to have originated poljrphyletically, that is, 

 independently in several groups. Hence we are constrained to class together in one family 

 all those species which possess them, and this arrangement will, we hope, be found to be 

 a satisfactory one. It is but a slight, though an important modification of the arrange- 

 ment followed by previous authors. Thus, the Desmacidonidse of Vosmaer include, on 

 the one hand, more than our family, in that he admits most of our Heterorrhaphidae, i.e., 

 species without chelse, while, on the other hand, they include less, in that he keeps 

 separate the Ectyoninte, which do possess chelae. This is an arrangement of which we 

 cannot at all see the justification, more especially with regard to the separation of the 

 " Ectyonidse," and in the present work we consider the old " Ectyonidfe " as a subfamily of 

 the Desmacidonidse under the name Ectyoninse. The presence in the Ectyoninse of 



1 Spong. Meerb. von Mex. pt. ii. p. 83. 



