Mr. H. J. Carter on the Polytremata. 211 



cient to distinguish it from tlie foregoing species ; while the 

 calcareous composition, superior aperture, reticulated sur- 

 face, with foraminated interstices, and heterogeneous spicular 

 contents of the cavity sufficiently ally it to them to justify 

 its being considered a Polytrema. It might be viewed as a 

 transition form between Polytrema and Planorhulina^ but can 

 never be considered a species of the latter, being more like the 

 " rough " Glohigerina^ in which there is a reticulated surface 

 but onhj one foramen at the bottom of each interstice. 



Filling up the crevices in the groups oi PoJytremautriculare is 

 a new species of Pachastrella (sponge) , which I would propose 

 to designate ^^ parasitica,'''' whose skeleton-spicule (tig. 17, a) 

 consists of a simple short shaft terminated by three arms, each 

 of which is twice furcated, together with a minute flesh-spicule 

 (fig. 17, i) formed of a bacillary shaft like that oi Dercitiis 

 niger, but longer and more thickly and minutely spined. It 

 is the habit of Pachastrella to creep into such recesSes, and 

 thus to follow closely upon the borings of a Cliona ; so that in 

 one instance I found Dercitus niger together with a Cliona in 

 the midst of a thick piece of branched coral which came from 

 Cuba. 



Polytrema planum J n. sp. PI. XIII. figs. 18 & 19. 



Test sessile, calcareous, solitary, colourless. General form 

 thin, flat, frondaceous, following in shape the surface on which 

 it may be growing (fig. 18, J). Surface even, smooth, tessel- 

 lated by a polygonal reticulation with foraminated interstices 

 of various shapes (fig. 19) ; margin irregular; aperture ex- 

 centric, circular in form, with raised thin margin (fig. 18, c). 

 Internal structure cancellous, one layer deep, corresponding 

 with the reticulation on the surface. Chambers or flat cancelli 

 sacciform or utricular at the margin. Contents of the cells 

 sarcodic. Size | of an inch in diameter, almost immeasurably 

 thin. 



Hah. Marine. On hard bodies (old coral, &c.), spreading 

 Melohesia-Y[kQj following in form that of the surface on which 

 it grows. 



Loc. Australia. 



Ohs. I have but one specimen of the species, which is on a 

 branch of old coral partly overgrown with Melohesia and other 

 algJB, sponge, &c., bearing OrbitoUtes, Polytrema 7niniaceu7n, 

 and almost every variety of Planorhulina vulgaris^ together 

 with Alveolaria and other minute forms of free Foraminifera. 

 The even reticulation with foraminated interstices hardly raised 

 above the surface, accompanied beneath apparently by a more 



