and Acapulco Sponges. 357 



well represented by the Cape species briefly described in the 

 ^Annals' {I. c. p. 393), for which I would now propose the 

 name of TracJiya durissima, as the genus was characterized 

 in 1870 {' Annals,' vol. vi. p. 178, pi. xiii. figs. 11-16). The 

 spiculation in both sections is the same, viz. a stout skeletal 

 spicule radiating from the centre, faced by a minute one 

 which, inserted between the pointed ends of the former, gives 

 a compactness to the surface ; both spicules are for the most 

 part acuate or pin-like, although the skeletal one in Trachya 

 pernudeata {op. et he. cit.) happens to be acerate ; while the 

 extreme compactness of the genus Trachya makes it resemble 

 Donatia lyncuriiim so much that the Cape species of Poly- 

 mastina (viz. Trachya durissima) might be easily mistaken 

 for it at first sight. Keller's Taherella, found in the Bay of 

 Naples, appears to me to belong to this section (Arcluv f. 

 mikroskop. Anatomic, Bd. xviii. S. 276, Taf. xiv. 1880). 



For Axos CUftoni I have provisionally proposed a group 

 under the name " Axona " {'■ Annals,' 1881, vol. vii. p. 381) ; 

 but, as already stated, the examination of the species Phorbas 

 amaranthus^ de F. et M., from the West Indies, has thrown 

 so much light on the Australian species Axona anchor'ata and 

 A.Jihdata, which were described from very " imperfect speci- 

 mens" ('Annals,' /. c. pp. 382, 383), that 1 would now relegate 

 thera to the group Halichondrina under the generic name of 

 ''Phorbas.'' 



Xenospongia. 



For Xenospongia j^ntdUformis, from Torres Straits, and 

 HaJicnemia patera^ Bk., a British species, there might be a 

 group named " Xenospongina," =Xenospongiado3, Gray 

 (" Arrangement of Sponges," Proc. Zool. Soc. 1867, p. 547). 

 See spiculation (PI. XII. fig. 32, a-c). 



Placospongia. 



Again, for Placospongia melobesioides^ from Borneo, Ceylon, 

 and South America, tliere might be a group named " Placo- 

 spongina," = Placospongiadas, Gray {op. et loc. cit. p. 549), 

 in which the skeleton-spicule is pin-like (PI. XII. fig. 33, a, 

 b), combined with a spinispirular flesh-spicule, like that of a 

 Suberite (fig. 33, e^f, i), faced and axiated (for the sponge is 

 branched) by a massive aggregation of elliptical siliceous 

 balls like those of a Geodia (fig. 33, c, ^), or mixed with a small 

 spherical subs]iined one like that of ChondriUa nucula (fig. 33, 

 (/, h) — thus uniting in spiculation two groups, viz. the Su- 

 berites, as above divided, and Geodina, in which the spicular 

 characters of the former preponderate. 



Ann. c& Mag. N. Hist. Ser. 5. Vol. ix. 25 



