GENUS MILIOLA. 79 



dering three chambers always visible externally- This is the true Triloculine form (Plate VI, 

 figs. 13, 14). 



108. Now although, if typical specimens only Avere compared, these characters might 

 well seem to be sufficiently definite to justify the generic differentiations which have been 

 founded upon them, yet the comparison of extensive suites of specimens brought from 

 different localities shows that they are subject to an inconstancy whicli altogether destroys 

 their value. And this inconstancy is readily accounted for, when due allowance is made for 

 the indefiniteness in the form of the sarcode-body of the animal ; since, as we have seen, it is 

 dependent upon the degree in which the " alar lobes" of the new segments extend themselves 

 over the surfaces of the preceding chambers, and on the equality or otherwise of the pro- 

 longations on the two sides — characters which are extremely liable to variation among 

 Foraminifera. Of those subordinate departures from the typical form of the segments, whicli 

 convert their ordinarily rounded outline (Figs. XV, a ; XVI, a, b ; XVII, a ; XVIII, a) into 

 a carinate or angular contour (Figs. XV, b, c ; XVI, c ; XVII, b, c ; XVIII, b) — differences 

 on which a vast multitude of specific differentiations have been founded — it can only be here 

 stated generally that they are subject to the same uncertainty as the larger ones already 

 disposed of. 



109. With such diversities in the form of the chambers are associated corresponding 

 diversities in that of the apcriure ; which may be elongated laterally so as from a circle tc 

 become an oval (which is sometimes narrowed into a mere slit), or may approach the form of 

 a square (Plate VI, figs. 8 — 12, 16 — 33). The shape of the "valve," again, varies with that 

 of the aperture, and has further variations of its own. In the MUiola cydostoma of Schultze 

 (xcvii, plate ii, figs. 14, 15), the valve is altogether wanting, and the aperture is quite round. 

 In the Spirohculina represented in Plate VI, fig. 1, the aperture, shown in fig. 16, has but a 

 very small projection ; this projection is a httle larger in the specimen represented in fig. 2, 

 of which the aperture is shown in fig. 17, and is somewhat extended laterally; and in the 

 QiiinquelocuUna represented in fig. 3, of which the aperture is shown in fig. 18, the valve is 

 distinctly bifid. In Bilocidlna the usual form of the "valve," as shown in figs. 7, 8, 10, 1 1, 12, 

 is that of a broad, rounded tongue, springing from the whole of one side of the aperture ; but 

 in the specimen shown in fig. 9, the valve, still much extended laterally, springs from a nar- 

 rower base. In figs. 1 9 — 32 is shown a very remarkable series of apertures and valves of a 

 large MUiola, from specimens brought by Mr. Cuming from the Philippine seas ; of which 

 variety an example is represented in fig. 33 broken open, so as to show the interior of the 

 last chamber, and to allow its aperture and valve to be seen from within, whilst the much 

 smaller aperture and simpler valve of the penultimate chamber are seen from without. This 

 series is particularly interesting, as showing the wide range of variation that exists in regard 

 to the form both of the aperture and of the valve, among a number of individuals whicli 

 must unquestionably be regarded as belonging to the same species ; some of the widest 



QmnquelocuUna and TrilocuUna . Neither of them, however, seems to have apprehended the essential 

 peculiarity of the real Triloculine type to be next described, although this had been correctly pointed 

 out by M. D'Orbiguy. 



