B. W. PRIEST ON THE HEXACTINELLIDCE. J 



mary one, and forming a new sub-order, the Callicispongice, the 

 former, Coralliospongice, comprising those sponges with a siliceo- 

 fibrous skeleton, the latter those whose skeleton is composed of an 

 interlacing spicular formation, never reticulate and continuous. 



Later on, in 1875, Mr. Carter, whose classification will, I think, 

 still hold good, retained the order Hexactinellidce of Schmidt, 

 dividing it into three families : — First, the Vitreo-hexactinelhdce, or 

 those sponges whose spicules are held together by silicified fibre ; 

 secondly, the Sarco-hexactinellidce, or those whose skeleton spicules 

 are held together by amorphous sarcode ; and thirdly, the Sarco- 

 vitreo-hexactinellidce, or those whose spicules are held together in 

 one part by vitrified fibre, and in the other by amorphous sarcode, 

 and which at present contains only one species. These, again, are 

 divided into six groups, namely, Patulina, Tubulina, Scopirfifera, 

 Rosettifera, Birotulifera, and the single species, Euplectella cucumer 

 of Owen, in the third Family. 



In all the Hexactinellidce known we find a minute flesh spicule in 

 the form of a rosette, which may be defined as an equi-armed, 

 sexradiate spicule, from the ends of whose arms proceed a certain 

 number of rays, which, although the same on each arm of the speci- 

 men, vary in form, number, and arrangement with the species, but 

 always project from the ends of the arms. These spicules often 

 afford, in conjunction with others, a means of specific distinction. 

 When I say that the spicules are formed on the hexradiate plan, I 

 mean that there is a primary axis, which may be long or short, and 

 at one point four secondary rays cross this central shaft at right 

 angles. Often one halt of the central shaft is absent or 

 shortened, or is represented by a rounded boss, and we 

 have then a spicule with a cross-shaped head, an often occurring 

 form in the defence and ornament of the surface layer of these 

 sponges. Sometimes the secondary rays may be partially or 

 wholly undeveloped, which occurs in young spicules and others 

 which are slightly abnormal, but in their place may be seen four 

 little elevations near the middle of the spicule, maintaining the per- 

 manence of the type. 



In some cases a fifth ray is developed, as in the surface layer of 

 Holtenia Carpenteri. At the distal end of the central shaft a rosette 

 similar to the flesh spicule may be found, as in Euplectella and 

 Dendrospongia. 



Those sponges which are found in the deep water ooze, as most 



