750 
THE VOYAGE OF H.M.S. CHALLENGER. 
Sub-family 4. Cycloclypeinse. 
Cycloclypeus, Carpenter. 
Cydodypeus, Carpenter [1856], Carter, Martin, Brady. 
The genus Cycloclypeus was instituted by Carpenter for the reception of certain dis- 
coidal Foraminifera of very large dimensions “ dredged by Sir Edward Belcher from a 
considerable depth of water off the coast of Borneo.” Since the publication of the original 
memoir containing the account of these recent specimens, 1 the structure and affinities of 
the genus have been further elucidated by the researches of Carter 2 and Martin, 3 upon a 
number of fossil species. Unfortunately the Challenger collections afford but little 
material bearing upon the subject. A few examples of a small but very interesting 
variety, however, have been met with in one of the dredgings, which may be best intro- 
duced by a brief indication of the prominent characters of the genus. 
The test of Cycloclypeus is a circular disk, either regularly biconvex, or umbonate at 
the centre, with a thin, sharp, peripheral edge. It is composed of concentric annuli, the 
boundaries of which, as well as those of the constituent chambers, are to a greater or less 
extent visible externally, being marked, especially near the margin, either by raised bands 
or by lines of clear shell-substance. The centre of the disk on both sides is often studded 
with raised beads or tubercles. The general aperture takes the form of a row of marginal 
pores. The texture of the shell of recent specimens is conspicuously hyaline and finely 
porous. 
Examined by means of sections, the test is found to be composed of three distinct 
portions, a central disk formed of a layer of chambers arranged in concentric zones, and 
two lateral plates of compact shell-substance, one on either side, enclosing it more or less 
completely. 
The chambers of the successive annuli of the central disk alternate in position more 
or less regularly, like those of an Orbitolite. The adjacent chambers of the same annulus 
do not communicate directly with each other, but each chamber communicates with two 
chambers of the preceding and two of the succeeding zone. The proportionate length and 
breadth of the chambers vary in different species and even in different specimens of the 
same species. 
The shelly plates which enclose the median disk above and below are variously 
developed, but always thickest at the centre. They sometimes attain twice or three 
times the thickness of the central layer, and in such cases the test assumes the form of a 
1 Phil. Trans., 1856, p. 555. See also Introd. Foram., 1862, p. 292. 
2 Ann. and Mag. Nat. Hist., ser. 3, vol. viii. pp. 332, 461. 
3 Untersuchungen iiber die Organisation von Cycloclypeus, Carp, und Orbitoides, d’Orb., von Dr. K. Martin, Nieder- 
landisches Archiv fur Zoologie, vol. v. pp. 185-204, pis. xiii., xiv. 
