Sponges from the Atlantic Ocean. 393 



('Ann.' 1870, vol. vi. p. 178, pi. xili. figs. 11, &c.), also esta- 

 blishing the genus at the same time. 



Others of a like nature exist in the British Museum from 

 Port Elizabeth in S. Africa ; and lately Mr. W. J. Sollas has 

 given me half of one, in form like a little bolster (viz. cylin- 

 drical and slightly constricted in the middle), said to have 

 come from Australia. It is 5 inches long and 2 inches thick. 

 Those which I have hitherto seen vary under this size, are 

 more or less globular, and each attached to a little stone. 

 They are intensely hard and tough, grey outside and light 

 yellow within, presenting a uniformly round form and stiff 

 villous surface, with no appearance of vents, or at least, if any 

 of the latter, very small, numerous, and indistinct. Internally 

 the structure is fibrous, radio-reticulate, traversed through the 

 interstices by the excretory canal-system, which is evident 

 enough here. As the branched reticulation radiates from the 

 centre, which is not nucleated, the fibre of which it is com- 

 posed becomes smaller and the interstices closer until a little 

 before it arrives at the circumference, where it is lost in a 

 dense mass of spicules that terminate in the villous surface of 

 the dermis. The spicules of which the reticulated structure 

 and the body generally arc composed are smooth, slightly 

 curved, and fusiform, rounded or inflated pin-like at one end 

 and more or less pointed at the other, faced by a smaller but 

 like form at the circumference, where there is no cortex 

 beyond the more densely packed state of the general structure- 

 My observations under Trachya pernucleata [l. c.) are equally 

 applicable here ; and these sponges, of which there may be 

 several species, will probably have to be considered a solid 

 Geodta-\ike form of Polymastia^ very nearly allied to the 

 Donatina, and all belonging to the suborder Suberitida. I 

 am very much inclined to think that although in some of the 

 species the spicule ap})ears to be acerate (that is, finely pointed 

 at both ends), a microscopical power of about 400 would show 

 that one end is slightly obtuse — that is, leading to the acuate 

 and pin-like forms with fusiform shafts of most of the species. 

 When one end of a linear spicule is rendered thus obtuse, it is 

 always at the expense in length, of this half of the spicule, so 

 that the maximum inflation of the shaft is thus thrown out of 

 the middle and nearest to the obtuse end. 



Polymastia stipitata^ n. sp. 



General form consisting of a head and long stem. Head 

 round at first, then obovoid with a papillary eminence on one 

 side of the large end; afterwards cylindrical, expanded upwards, 



Ann. & Mag. N. Hist. Scr. 4, Vol. xviii. 27 



