190 Mr. H. J. Carter on the Polytrenuita. 



simple or branched; while internally this structure is sup- 

 ported on processes which rest on a thin chitinous layer that 

 adheres to the object on which the specimen may be growing. 

 Thus constituted, the foraminated surface and cancellated struc- 

 ture extend upwards into the short cylindrical process men- 

 tioned, which, presenting a single tubular aperture with round 

 inflated rim, terminates the young Polytrenia in this direction, 

 (fig. 4,^). But as the upper part of this cylindrical process 

 consists of a single thin foraminated layer of a tubular form, it 

 is very delicate, and is thus often broken off down to where the 

 interior begins to pass into the cancellated structure, and thus 

 becomes stronger (fig. 4, e). Here we may observe, on looking 

 endwise into the truncated end, that the cylindrical process is 

 divided into three or more portions (fig. 5), each of which is 

 successively larger than the foregoing one ; so that the last 

 (which nearly embraces all the rest, and thus occupies two thirds 

 of the circle on one side, while the three others occupy the 

 other third) completes the circle as it grows above them into 

 the delicate foraminated tubular layer, which ends in the single 

 aperture above mentioned. It is thus in the " truncated e\\^ " 

 that we seem to be able to trace a resemblance to the spiral 

 growth and successive enlargement of the primary chambers 

 manifested in the Foraminifera generally, more especially in 

 those which belong to the discoid type. As the young Poly- 

 trema increases in size, new circumferential layers are added 

 until a mass is produced which passes into a thick round stem 

 with several branches (fig. 1). Hence the original single axis 

 becomes divided into as many as there are branches, each 

 of which is but a repetition of the original one in point of 

 development. 



Although the " truncated end " of the cylindrical process 

 (fig. 5) in the young Polytrema seems, by its multilocular struc- 

 ture and arrangement, to indicate a spiral mode of growth, I 

 have never been able to recognize a spiral arrangement of 

 the lines presented by the base of a Polytrema — although on 

 one occasion a subsequent concentric arrangement of these 

 lines seemed to indicate a spiral beginning, as such an ar- 

 rangement often follows a spiral one in many specimens of the 

 discoid Foraminifera. However, as this did occur, although 

 only in one instance, which has been dry-mounted, I will 

 now briefly describe it. 



The specimen, a small branched one, had been overgrown 

 by the horny fibre of Ghalina oculata (sponge), through the 

 former having previously attached itself to the hard object 

 subsequently selected by the latter. Consequently when the 

 sponge (an insignificant fragment picked up on one of the 



