and the Sjjoyige-spicules o/" Poly trema. 391 



examination by Dr. Carpenter, the above heterogeneous assem- 

 blage is fomid the minute stellate and smooth pin-like spi- 

 cules preponderating. On the other hand, in and about some 

 specimens of Folytrema on a crab-claw, which Dr. Carpenter 

 also gave me, the preponderating spicule is club-shaped spi- 

 nous, with anchorate spicules (of the kind mentioned hereafter), 

 with the points, and not the heads, of the former projecting 

 outwards — evidencing by this and their preponderance that 

 the sponges which these two combinations respectively repre- 

 sent grew on the Polytrema accidentally, and not parasitically. 



Of course, if Polytrema is in the habit of drawing to itself 

 sponge-spicules, which, from the vast number of sponges always 

 growing, dying, and disintegrating at the bottom of the sea, 

 must be almost as plentiful as grains of sand there, it is not 

 strange that the spicules which to-day are matted among its 

 pseudopodia on its surface should, in a few days after, be found 

 in the interior of its calcareous structure ; and hence the pre- 

 sence more or less of sponge-spicules thi-oughout the latter 

 may be explained. Moreover, in addition to sponge-spicules, 

 there are frustules of Diatomaceje, fragments of minute Crus- 

 tacea, and the minute, clathrous, calcareous bodies of the 

 fleshy parts of Echinodermata, — in short, just as in Squamu- 

 lina^ almost any thing and every thing of this kind that may 

 pass in its way. At the same time, the amount of spicules 

 and their variety will vary in the structure of the test of Poly- 

 trema with the amount of sponges and their variety in the 

 locality in which it may grow ; and hence at one time there 

 may be an excess and at another a comparative deficiency of 

 spicules*. 



Lastly, as regards the arborescent form of Polytrema^ com- 

 pared with Schmidt's Haliphysema ramuhsa from Florida, 

 the former is massive, extending here and there into short 

 projections which may be termed pseudo-branches, while 

 Schmidt's specimen is slender, dendritic, and dichotomously 

 branched three times. For this species Schmidt has proposed, 

 on his slide, the name of '''' Lojplialia affinis,'' instead of " Hali- 

 physema.^^ 



It seems also desirable that the spicules preponderating so 

 excessively beyond all others on the specimens of Polytrema 

 should be particularized, as they evidently belong to two dis- 

 tinct sponges, hitherto, apparently, undescribed. 



That in the fragments taken from Mr. Macdonald's speci- 

 mens of Polytrema by Dr. Carpenter presents a combination 



* See also Gray on Poh/trema in Proc. Zool. Soc. 1858, p. 270, and 

 Ann. & Mag. Nat.'llist. 1858, vol. ii. p. .386; Max Schultze, Ann. & Mag. 

 Nat. Hist. 186.3, vol. xii. p. 409, and Gray, ihid. 1864, vol. xiii. p. 111. 



27* 



