and the Sponge-spicules of Poly trema. 391 



examination by Dr. Carpenter, tlie above lietcrogeneous assem- 

 blage is found the minute stellate and smootli pin-like spi- 

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

 specimens of Poh/treina on a crab-claw, which Dr. Carpenter 

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

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

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

 outwards — evidencing by this and tlieir preponderance that 

 the sponges which these two combinatioiis respectively repre- 

 sent (jrew 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 num])jr 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 wliicli 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 adlition to sponge-spicules, 

 there arc tVustules of Diatomacea^, fragments ot 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 stnicture of the test of Poly- 

 trema with the amount of sponges and their variety in the 

 locality in Avhich 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 ramulosa 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 '•^ Lophatia affi.nis^^'' instead of " Hali- 

 physema.^'' 



It seems also desirable that the spicules preponderating so 

 excessively beyond all others on the specimens of Polytrema 

 should be ])articularized, 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 nrav on Pnh/frema in Proc. Zool. Soc. I808, p. 270, and 

 Ann. & Mag. Nat.'llist. 18-58, vol. ii. p. 386; Max Schultze. Ann. & Mag. 

 Nat. Hist. 1863, vol. xii. p. 409, and Grav, ibifi. 18(>1, vol. xiii. p. 111. 



27* 



