Mr. H. J. Carter on the Polytremata. 189 



cimen, which, arising in the confines of the test, finally com- 

 municate with the apertures at the ends of the branches ; hence 

 the masses of spicules and grains of sand which they often 

 contain (fig. Q^vvv) can be easily explained ; together with 

 other spicules, which, having become incorporated during 

 growth, more or less traverse the test generally — the whole 

 of the structure internally being lined with sarcode, which, 

 according to Max Schultze (who had recent specimens to deal 

 with, l. c. p. 411), is in the form of chambers opening into 

 each other by stolon-like constrictions, through which they 

 not only intercommunicate but are successively produced 

 ('Annals,' 1863, vol. xii. pi. vii. figs. 4-8). Still, although it 

 is easy to see how these chambers communicate with the caver- 

 nous dilatations or cavities in the midst of the reticulated struc- 

 ture in the oZfZ specimens, where the sarcodic lining has become 

 thickened and dried into a chitinous layer, it is not so easy 

 to see how it takes place in the younger specimens, where the 

 foraminated interstices have not become absorbed and the sub- 

 concentric layers (fig. 3, a a a) of which the test is formed 

 apparently permit of no other communication between their 

 cavities. Size of largest specimens (which, for the most part, 

 have their branches broken off) 3-24ths inch in diameter and 

 2-24ths inch high. 



Hab. Marine, on solid objects, chiefly stony coral. 



Loc. Mediterranean ; Red Sea ; West Indies ; Mauritius ; 

 Torres Straits ; Australia ; Polynesia. 



Obs. There are two forms in which Polytrema miniaceum 

 is found, viz. massive and branched ; but the former appears 

 to me to differ from the latter merely in the branches having 

 been broken off, in which the remaining portions thus trun- 

 cated have provided themselves with the form of apertures 

 above mentioned (fig. 6, bb). The branches, which seldom 

 undergo a second division beyond a divided grouping of the 

 apertures at their extremities (fig. 6, a a a), vary in number 

 from a few to a great many, in which case the specimen some- 

 times presents a head of branches almost as closely approxi- 

 mated as those of a cauliflower. 



Following the mode of growth in a specimen of Polytrema 

 miniaceum not more than l-80th inch in diameter at the base, 

 and about l-83rd inch high (fig. 4), it may be observed at this 

 period to present a circular patch or base of cancellated struc- 

 ture (fig. 4, a), rising up in the centre into a short cylindrical 

 process (fig. 4, J), the whole of which is thickly though minutely 

 foraminated on the sui-face,and more or less divided and dimpled 

 by an unforaminated network of lines, whicii give to the in- 

 terstices shapes varying from circular to submcandriniform, 



