2 Mr. H. J. Carter on three Puchylragous Sponges 



Thus I find that it is only wlien a portion of Pachymatisma 

 is torn from its natural place of growth, and becomes free in 

 the sea, that it assumes a spheroidal form. S])reading hori- 

 zontally in its natural habitat, on inclined surfaces, in the 

 most sheltered bowers of the shore-rocks, it rises more or less 

 into obtusely rounded eminences, which give to its sur- 

 face a deeply undulated fomi. This surface, too, as is well 

 known, is incrusted with a cortical layer or zone of globular 

 crystalloids, which, although thickest on its free side, is never- 

 theless continued all round the sponge, and frequently extends 

 some distance into the mouths of the larger exhalant apertures 

 or oscules ; while the exhalant system of canals is also more 

 or less horizontally developed, and not radiating, in accordance 

 with the mode of growth of the sponge. Hence, when a por- 

 tion becomes detached from its natural habitat and free in the 

 sea, it soon surrounds itself entirely with the thick incrusta- 

 tion ; while, its excretory canal-system and general structure 

 continuing as before internally, it can have no radiated ar- 

 rangement of the latter, however much its form may become 

 spheroidal externally. The same applies to the Tethyada?, of 

 which T. cranium is the type. Thus it may be observed, in 

 my description and illustrations of T. arahica (Annals, vol. iv. 

 p. 1, 1869), that 1 found specimens of this species growing in 

 a fixed hemispherical and in a free subspherous form respec- 

 tively. But, as the fixed form has a radiating structure, so, 

 when a portion has been detaclied from the rock (for it may 

 be assumed always to commence life in a fixed form), it retains 

 this radiated structure in the spheroidal one. Then, as the 

 spheroidal form is accidental in both the free specimens of 

 Pachymaiisma Johnstonia and Tethya arahica, we cannot pro- 

 perly call them " subspherous s])onges." This, too, may be 

 the case with the Gcodidtc and Tethyadaj generally. 



The only true instance of a spheroidal sponge is seen in Tethya 

 lyncurium and the like, where the sponge grows into this form 

 on a pedicel, — and here not always, as some of the specimens of 

 this sponge which grow on the rocks of this place demon- 

 strate. At the same time it should be remembered tliat this is 

 not a TetJiya, if we are to regard T. eranium as typical of the 

 Tethyadic ; and hence Ui-. Gray has very properly adopted 

 Nardo's name of " Donatia^'' for this genus (?. c. p. 541). 



Still it may be asked how it is that the spheroidal specimens 

 of Tethya lyncurinm, when cast upon the shore, always pre- 

 sent a facet from which the pedicel has been broken off, while 

 no such indication of ])rcvious attachment ap])ears on the sub- 

 s))herous specimens of Tethya proper, Geodia, and Pacltyma- 

 tisma (see my illustrations, ' Annals,' I. c). 



