GEiniS PENEEOPLIS : — OEGAJVIZATION. 
5 
these variations are not indicative of any specific difference, is at once proved by the 
fact that the shells which exhibit them in one part, present the ordinary character of 
surface in another. In Plate II. fig. 22 is shown a case in which similar punctations 
present themselves on the septum closing the mouth of the shell of a Bendritina, which, 
as wall presently appear, is only a modified Peneroplis. 
125. The septum which closes the mouth of the shell is perforated by numerous 
isolated pores, arranged in a single linear series (Plate I. fig. 2, Plate II. fig. 1); the 
number of these pores depends upon the length of the septal plane (a very convenient 
term which I adopt from Professor Williamson), and thus it usually increases with 
the age of the indmdual, each chamber opening externally by a larger number of pores 
than did that which preceded it. The typical form of these pores seems to be circular, 
though they are apt to present various departures from that shape ; they usually lie in 
a sort of furrow, formed by the projection of the lateral borders of the mouth somewhat 
beyond the septum ; and, as in Orbitolites and Orbiculina, each one is surrounded by a 
prominent annulus of shell. 
126. The texture of the shell very closely resembles that of Orbitolites and Orbiculina^ 
but is somewhat more porcellanous. As in those genera, the shell presents an opaque 
white hue, when it is viewed by light reflected from its surface ; whilst thin sections 
examined by transmitted light are of a brownish yellow or dark amber colour. Its sub- 
stance is apparently quite homogeneous, no other trace of structure presenting itself 
than the plications and punctations already referred to ; and its texture is not nearly so 
fii-m as that of those Foraminiferous shells which possess a minutely-tubular organi- 
zation. 
127. On examining a thin section of a typical Peneroplis, taken through the median 
plane between the lateral surfaces (Fig. I.), the central chamber is seen to have the 
rig. I. 
Section of Peneroplis, parallel to its surface. 
globose form which has been shown to characterize the primordial segment of the Fora- 
minifera already described ; from this first chamber a single passage leads to the second. 
