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THE VOYAGE OF H.M.S. CHALLENGER. 
cenomana. Of the first of these no descriptive characters are given, nor any reference 
to published figures, so it may be entirely ignored ; of the second, Placopsilina 
cornueliana, no description is given, but reference is made to some very characteristic 
drawings in Cornuel’s memoir on Cretaceous microzoa ( loc . cit.) ; whilst to Placopsilina 
cenomana nothing but the following note is appended : — “ Espece contournee en crosse 
adhcrente aux corps.” That the two latter specific terms are synonymous, and apply 
to mere individual modifications of the same typical form, there cannot be any doubt ; 
and it is a matter for regret that the ill-defined “ cenomana ” should have been 
perpetuated by Reuss, to the exclusion of a name founded on an authentic figure and 
dedicated to the discoverer of the organism. 
Placopsilina cenomana is a very variable species. The test consists of a single line of 
chambers generally arranged at its commencement in a flat spire, but diverging at a later 
stage and taking a straight, curved, or very irregular course. Hence it may be entirely 
spiral like an attached Truncatulina, or crosier-shaped, or indefinitely spreading, the 
contour depending in part on the nature of the body to which it is attached. 
The species differs from the allied Bdelloidina aggregata in that the chamber-cavities 
are undivided and the aperture single, whilst the latter form has labyrinthic chambers 
and a porous aperture. Its closely approximated chambers and rough exterior serve to 
distiuguish it from the isomorphous Webb m a irregidaris, which has rounded and distinct 
segments and a comparatively smooth surface. 
Placopsilina cenomana occurs at one “Porcupine” Station, west of Ireland, 670 
fathoms, which supplies the only record of its existence in the North Atlantic. It is 
named in one of Parker and Jones’s distribution tables at two localities in the Mediter- 
ranean, — off Crete, 360 fathoms, and in Suda Bay, Crete, 40 fathoms ; and I have 
specimens from the late Mr. M‘Andrew’s dredgings in the Gulf of Suez, 30 fathoms. 
It has been found at one Challenger Station in the South Atlantic, south of Pernambuco, 
350 fathoms, and at five or six amongst the coral-reefs of the Pacific, at depths varying 
from 3 fathoms to 35 fathoms. It is by no means a common form, except in the 
shallow water of tropical and subtropical seas. 
The geological history of the species commences with the Lower Lias marls of the 
west of France : it is found in the Middle and Upper Lias of both France and England, 
and again in the Lower Oolite ; also in Cretaceous deposits of various ages in numerous 
localities in France and in the Eastern Alps ; but there does not appear to be any record 
of its existence in formations of later geological age. 
Placopsilina vesicidaris, H. B. Brady (PI. XXXV. figs. 18, 19). 
Placopsilina vesicularis, Brady, 1879, Quart. Journ. Micr. ScL, vol xix., N. S., p. 51, pi. v. fig. 2. 
Test irregular in shape and size, spreading in indefinite patches over stones ; usually 
