AND ITS INTERNAL STRUCTURES. 313 



The genus Tretomphalus is related to Discorhina. The acquisi- 

 tion of the perforated bosses in addition to the customary 

 pseiidopodial perforations speaks for itself as a strongly marked 

 advance on the Discorhina type. The internal tube opening 

 points to the simple Entosolenia type." 



Brady devotes a considerable space to Cymhalopwa hulloides in 

 his report on the Foraminifera of the Challenger expedition (D), 

 and as his description summarises all that was known of the 

 species at this time, I will quote its more important parts. He 

 writes : " The salient feature of C. hulloides is the large inflated 

 chamber which forms the base of the shell, and constitutes the 

 greater part of its entire bulk. In its earlier stage the test is 

 Rotaliform, the superior side convex, the inferior concave ; the 

 segments are arranged in about three convolutions, and but 

 for a certain irregularity in the disposition of the later whorls, 

 it might in this condition be mistaken for one of the weaker 

 modifications of Discorhina. The inferior side of the Rotaliform 

 shell has an umbilical depression, round which the segments are 

 arranged, and into which they open, and the intervals between 

 the chambers form radiating fissures. In all these points the 

 initial test resembles the typical C. 2^oeyi, but the general contour 

 is more outspread and the umbilical recess remains open, not 

 being covered by a shelly flap, as is usual with the latter species. 

 The peripheral margin of the Rotaliform test forms the line of 

 attachment of the large balloon-like chamber which envelops 

 the whole of the inferior side. The distal face of the " balloon " 

 is decked with a number of large, Orbuline pores, the margins of 

 which have generally a slight rim or border. Moebius has 

 pointed out that one of the pores near the centre of the disc is 

 furnished w^ith a short tube, projecting into the cavity of the 

 chamber, and suggests that this constitutes the general aperture 

 of the test. The existence of this Entosolenian orifice had been 

 overlooked by previous writers, but I am able to confirm the 

 observations of Moebius in every particular, having seldom failed 

 to trace it, except in occasional very small specimens. It often 

 cannot be detected externally, but sometimes it is situated in a 

 little dimple or depression . . . and it may nearly always be 

 distinguished in balsam mounted specimens, when examined by 

 transmitted light. The test attains a diameter of ^V inch or more. 

 C. hidloides has long been known as a bottom foraminifer . . . 



