324 
THE VOYAGE OF H.M.S. CHALLENGER. 
This is an exceedingly rare species. The test is of smaller dimensions than that of 
the typical Thurammina papillata ; the walls are relatively thicker, and constructed of 
finer materials less compactly cemented. The nearly white colour is also a very 
distinctive feature. The little mammillate protuberances, instead of being numerous and 
distributed irregularly over the surface, are few in number, and placed more or less 
symmetrically. 
The only locality in which more than a single specimen of Thurammina albicans has 
been met with is Station 323, off the coast of South America, in about the latitude of 
Buenos Ayres, depth 1900 fathoms ; and even there it is by no means abundant. 
Haeusler mentions the occurrence of fossil specimens presenting similar characters in 
later Jurassic rocks of Switzerland. 
Thurammina compressa, H. B. Brady (PI. XXXVII. fig. 1). 
Thurammina compressa, Brady, 1879, Quart. Journ. Micr. Sci.. voL xix., N. S., p. 46, pi. v. fig. 9. 
Test rounded, compressed, sublenticular ; with numerous perforated mammillate 
protuberances arranged irregularly on the periphery. Walls thin, chitino-arenaceous ; 
colour dark-brown. Diameter about -g^th inch (0'5 mm.). 
This also is a scarce modification of the type. It is distinguished by its membranous, 
only slightly arenaceous test, and its compressed almost lenticular contour. It is possible 
that the latter character may be in a measure accidental, and due to the partial collapse 
of the more or less flexible walls, as not unfrequently occurs in other chitino-arenaceous 
forms, as, for example, in Trochammina macrescens. At the same time, the position of 
the mammillate orifices, on the peripheral margin, and not on the lateral faces of the test, 
makes it more likely that the natural form is retained by the dried specimens. 
Thurammina compressa has only been found at a solitary Station in the North 
Atlantic, south of the Bockall Bank, 630 fathoms. 1 
Hippocre'pina, Parker. 
Ilippocrepina, Parker [1870], Brady. 
As only a single species of this genus is known to zoologists, the generic and specific 
characters may be included in the same description. 
1 In the preliminary account of this species, the depth was accidentally misstated. 
