340 Mr. R. Hope on two neiv 



at each end; measuring on the average about '188 x "005 

 millim. (fig. B, 3). 



MtC7'oscIera{?). — There are present in places, chiefly near 

 the surface of the sponge, a few long and exceedingly fine 

 styles, sometimes microspined at the base. They are very 

 few and appear to be local in their distribution in the sponge 

 and wanting altogether in many parts of it ; probably they 

 are to be looked upon rather as varieties or immature forms 

 of the megasclera. 



From what has been stated it will be seen that this sponge 

 agrees with the species of the genus Trachytedania in the 

 possession of a skeleton composed mainly of spined styles and 

 smooth tylota ; that genus also already comprises as one of 

 its two species a thin incrusting sponge, T. spinata (P. Z. S. 

 1881, p. 122), with a skeletal structure of the kind which is 

 frequently present, with some comparatively slight modifica- 

 tions, in sponges of that habit, and closely similar to that of 

 the sponge under consideration. There is, however, no echi- 

 nating spicule in T. spinata^ and it is by the possession of a 

 special spicule of this nature, the straight, entirely spined 

 styles, that T. (?) echinata differs most markedly from the 

 other two species of the genus. 



In some groups of the family Desmacidonidaa, R. & D., 

 this seems to be a feature of minor importance (see ' Chal- 

 lenger' Monaxonida, p. 129, and siqrra, p. 337) ; whether it 

 is so also in this case, the data afforded by so small a series of 

 forms appear to me insufficient to base a decision on them. 

 The absence of trichites would present another point of diver- 

 gence from the diagnosis of the family Tedaniinas, R. & D. 

 (' Challenger ' Monaxonida, p. 50), if the few long and fine 

 spicules which are present here be, as seems most likely, 

 merely modifications of the megasclera ; this difference, how- 

 ever, seems of less importance, as the same doubt as to the 

 nature of the " rhaphides " in the closely allied genus Te- 

 dania is expressed by Messrs. Ridley and Dendy (' Chal- 

 lenger ' Monaxonida, p. 56) ; the oxeote spicules, smooth or 

 microspined, which are present in some of the species of 

 Tedania and which are noted in Dr. Gray's original diag- 

 nosis (P. Z. 8. 1867, p. 520), are absent both in this sponge 

 and in the other species of Trachytedania^ the fine spicules in 

 the latter, whatever their nature, being respectively stylote 

 (P. Z. S. 1881, I. c.) and " oxeote slightly thicker at one end 

 than the other ^' (' Challenger' Monaxonida, p. 57). It may 

 be remarked that what may perhaps be homologous spicules 

 abound in some species of the Clavulinse (e. g. Suberites 



