GENUS PENEKOPLIS : OEGANIZATION. 



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 Dendritina, which, 

 as will 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 individual, 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 

 firm 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 



Fig. 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, 



