4 DE. CAEPENTEE'S EESEAECHES ON THE FOEAMINIFEKA. 



Mr. CUMING'S Philippine Collection ; whilst the most numerous were kindly furnished 

 me by Mr. J. GWYN JEFFERYS from his dredgings in the Gulf of Genoa. We shall 

 hereafter find that, as in the case of Orbitolites, particular varieties of conformation 

 prevail, though by no means exclusively, in particular localities. 



123. External Characters. The ordinary form of the shell of Peneroplis (of which an 

 ideal representation is given in Plate I. fig. 2) is an extremely flat spire of about two 

 turns and a half, opening out rapidly in its last half turn (Plate II. fig. 1). In the 

 young shell, each whorl is merely adherent to the preceding, so that the first-formed 

 portion is not concealed by the subsequent growth ; but it very commonly happens that 

 the last whorl spreads itself out to such a degree as partially to invest the preceding 

 (Plate II. figs. 1, 3), the extension towards the centre, however, seldom reaching so far 

 as to conceal the original umbilicus. Although this lateral extension is sometimes con- 

 fined to the inner margin of the spire, as is seen in fig. 1, yet it often occurs along the 

 outer margin also, as is seen in fig. 3 ; being usually limited, however, to the last four 

 or five chambers. But sometimes, instead of opening out and partially investing the 

 previous whorls, the spire is prolonged in a straight line, and several of its successive 

 chambers present little or no progressive increase in size (Plate II. fig. 5) ; though even 

 in this variety the last four or five chambers are often seen to spread themselves out 

 rather suddenly, so as to extend along the inner margin of the straight portion. Between 

 these different extremes of conformation, every intermediate gradation presents itself. 



124. The surface of the shell is very strongly marked by depressed bands, which 

 indicate the place of the septa between the chambers ; and between these septal bands 

 the walls of the chambers rise in flattened arches. In a direction transverse to the 

 septal bands, we almost uniformly observe a strongly-marked striation ; the striae running 

 parallel at tolerably regular intervals, which average about TTtfoth f an inch, from one 

 septal band to another. This striation, which imparts a very characteristic physiognomy 

 to these minute shells, seems due to a sort of plication or ridge-and-furrow arrangement 

 of the shelly wall (Plate II. fig. 20), which may not improbably have the effect of 

 imparting to it increased strength. The plication generally disappears at the junction 

 of the walls of the chambers with the septa ; and consequently we do not usually see it 

 at the mouth when the shell is viewed endways. Sometimes, however, it is continued 

 on to the septum itself; and its character is then extremely well displayed, as in Plate II. 

 fig. 15, which, however, represents not the typical form, but one of the varieties to be 

 hereafter noticed. On the prominences of the plicae, there are frequently to be seen 

 rows of extremely minute puncta (fig. 20) ; these, however, are not the apertures of pas- 

 sages through the shell, as might not unnaturally be supposed ; but are, like the punc- 

 tations of Orbiculina (^[ 88), mere depressions of its surface, as I have ascertained by 

 the careful examination of very thin sections. It is remarkable that the plication of 

 the shell is sometimes wanting, though the punctations may still present themselves in 

 rows, as shown in fig. 23 ; whilst in other cases, not only are the plicae deficient, but the 

 punctations are distributed uniformly over the entire surface, as shown in fig. 24. That 



