210 Mr. H. J. Carter on the Poljtremata. 



of the test, may have thus been faced with a foraminated 

 lamina, like the interstices of the reticulated structure forming 

 the concentric or successive layers of Polytrema miniaceum 

 and P. halaniforme respectively., 



Polytrema utriculare^ n. sp. PI. XIII. figs. 11-16. 



Test fixed, calcareous, colourless or whitish grey, gregarious. 

 General form globular, bottle- or sac-shaped (figs. ll-14), with 

 the aperture generally single and more or less superior (fig. 12, 

 bbb), supported on a short neck, rounded and inflated at the 

 margin and expanded at the base, where it becomes continuous 

 with the bottle-shaped body (fig. 13, a a a). Surface cribri- 

 form, commencing a short distance from the neck in a sub- 

 hexagonal bee's-comb-like network, so much in relief that the 

 foramina which fill the interstices at the bottom can hardly 

 be seen except by direct view (figs. 12 & 15). Internal struc- 

 ture consisting of a large, single, unseptate, globular cavity, 

 corresponding with the external form, and surrounded on all 

 sides but the base by the cribriform structure mentioned (fig. 15), 

 which, when viewed in a vertical section, shows that the bee's- 

 comb-like network (figs. 15, a, & 16, a) rests upon the fora- 

 minated layer (figs. 15, b, & 16, b) in the proportion of two to 

 one, the whole being 3-830ths of an inch in thickness. Cavity 

 lined by a sarcodic layer of a chitinous aspect when dry 

 (fig. 14, e), open at the aperture and closed below, where it 

 forms the bottom of the sac-like or bottle-shaped body, which 

 is thus attached to the object on which the species may be 

 growing. Filled more or less with siliceous sponge-spicules 

 and calcareous grains of sand, which, together with othe)- 

 minute objects, are agglutinated by sarcode into a mass 

 that presents a yellowish or dark-brown amber-colour when 

 dry (fig. 14,^). Size variable, as the sac-like body varies in 

 form : body of the most regularly formed specimen that I 

 possess about l-24tli inch in diameter, and about the same 

 high, including the neck and aperture. 



Hub. Marine. On hard objects (old coral &c.). 



Log. Tropics? 



Obs. The utricular body of this species is subject to great 

 variety in form, owing to the various influences that may 

 affect it during growth. When on a free surface, however, 

 it is generally bottle-shaped, globular, with superior aperture. 

 Sometimes the latter is double, as may be seen by the illus- 

 tration, wherein there are four apertures and only three chambers 

 (fig. 12, bbbb). The single unseptate chamber and the pro- 

 minence of the reticulated structure on the surface are suffi- 



