378 MESSES. E. HEEON-ALLEN AND A. EAELAND ON THE 



projecting at a divergent angle from the wall of the shell and pointing in the direction 

 of the aboral extremity (figs. 18, 19, 20). These projecting spicules, which to some 

 extent mar the symmetry of the test, are, perhaps, inserted with the definite purpose 

 of supporting the shell in an erect or vertical position in the surface-layer of mud with 

 its aperture uppermost *. 



Owing to the fact that the walls of the chambers are only one spicule thick, the 

 organism is of an extremely friable character, and fragments are much more commonly 

 met with than perfect specimens. 



Nouria harrisii varies greatly in size according to the locality of origin, but is fairly 

 constant at each locality. The Cebu specimens are the most typical, and average 

 I'l mm. long by "4 mm. broad. The specimen from the Caribbean Sea was consider- 

 ably larger, while the individuals from the Sahul Bank, Timor Sea, were of variable 

 sizes, but all much smaller than the Cebu specimens. 



Nouria compressa, sp. n. (PI. XXXVII. figs. 21-26.) 



Test free, highly compressed, consisting of 2-5 chambers rapidly increasing in size 

 and arranged biserially, the walls of the test consisting of a single layer of sponge- 

 spicules neatly cemented together into a smooth and finished surface. A grain of 

 sand or glauconite is occasionally used to fill in a crevice between spicules (figs. 22 

 & 25). Marginal edges acute and usually smooth and unbroken, especially at the 

 -oral extremity of the shell. Less neat at the aboral end, where there is often a 

 marginal fringe of projecting spicular points. Sutural lines nearly flush and obscure, 

 but generally well marked, owing to the divergent angles at which the spicules are 

 arranged in adjacent chambers. Aperture a neatly constructed terminal slit, sometimes 

 with a slightly raised border or lip of cement (figs. 21, 23). Internal septa con- 

 structed of spicules and often incomplete. 



In company with iV". harrisii in the dredging from Cebu (120 fms.) were found a 

 limited number of specimens which appear to be a highly compressed modification of 

 that type, isomorphous with Bolivina. The structure of the shell as regards the 

 employment of sponge-spicules as building-material is identical, and the arrangement 

 of the chambers is very similar, but, instead of being cylindrical or subcylindrical in 

 section, the tests are compressed and bi-convex, with acute marginal edges. 



N. compressa exhibits one or two differences in its mode of construction, probably 

 due to the difficulty of accommodating sponge-spicules to the peculiar shape of the 

 flattened test. Eound the edges of the test advantage is taken of the form of the 

 spicules to obtain an unbroken periphery, but this often entails that the terminal ends 



* This plienomenon may be compared with the arrangement of the spicules in the Crinorhiza form of 

 deep-sea sponoes. to which attention has been called by Prof. Dendy [' Outlines of Evolutionary Biology,' 

 (London, 1912), p. 335, fig. 168], as an obvious adaptation which serves to prevent the sponge from sinking 

 into and being smothered by the soft mud or ooze which covers the bottom of the ocean. 



