80 FAMILY MILIOLIDA. 



divergences being presented at the apertures of the successive chambers of one and the same 

 individual, as seen in fig. 33. In no two are the valves exactly alike in form ; and yet it is 

 obvious throughout that they are constructed (so to speak) upon the same model. They all 

 possess, in a more or less developed condition, a vertical plate or keel, which rises fi-om the 

 median line of the horizontal part of the valve ; and this keel, as is seen in the oblique view 

 given in fig. 30, frequently forms a sort of arch hollowed beneath like a bridge. In fig. 28 

 Avill be noticed a remarkable development of two pi'ocesses from the projecting angles of the 

 aperture, which are seen in a rudimentary condition in several other figures. In fig. 31, the 

 valve is so much extended horizontally, and the aperture is so unusually contracted, that 

 what should be the free margin of the valve has come to coalesce completely in one part, and 

 nearly to do so in another, with an ingrowth from the margin of the aperture ; thus distinctly 

 tending towards the formation of a complete septum perforated with separate pores, such as 

 we find in certain other modifications of the 3Iilioline type (•[■[ 110, 111, 118). 



1 10. A more remarkable departure from the ordinary type of aperture than any of the 

 preceding, is presented in the CrucilocuUiw o{ D'Orbignj'; which is a well-marked " triloculine"' 

 Miliola (fig. 15), of which the aperture has (so 40 speak) four small valves instead of one, a 

 crucial fissure being left between them. This extreme variety is very rare, being only known 

 to occur in the coast of Patagonia ; but approaches to it arc met with elsewhere. Another 

 remarkable departure from the ordinary type of aperture is occasionally found in the well 

 known " quinqueloculine " Miliola of the Grignon tcrtiarics (the MiHolHe>< mivoriai/ of Lamarck, 

 the QiniiquelocitHna saxorinii of D'Orbign}'), the \\ alls of whose chambers are often so thick as 

 to leave but little space for the sarcode-body, which is further encroached on by ridges that 

 project from their inner surface ; the aperture is much contracted and its " valve "' small ; and 

 sometimes the internal ridges, coming up into the aperture and coalescing with the valve, 

 form a cribriform septum that seems to foreshadow that of Faljidaria (to which type this 



, variety presents an obvious tendency) and of Peneroplis. We shall presently see that a 

 more perfectly-developed cribriform aperture is one of the principal features of the sub- 

 genus Haueriiia. 



111. Not less variable in this genus is the surface-marking of the shell ; for, although 

 normally smooth and sometimes highly polished, it often presents a scabrous aspect, and is 

 sometimes marked by a more or less regular pattern, formed either by longitudinal ribs as in 

 Plate "N'l, figs. 3, 4, 33, by transverse plications extending to the interior of the chamber as 

 in fig. 5, by minute pits arranged in longitudinal series as in fig. 14, by a honey-comb 

 areolation as in fig. 13, or by various modifications and combinations of these plans. Now 

 although such well-marked specimens as the four here figured might be reasonably considered, 

 if taken by themselves, as distinct specific types, yet the comparison of a sufficiently large 

 number of individuals necessitates the abandonment of any differentiation founded upon the 

 characters they respectively present ; for it is shown by such comparison that all these kinds 

 of ornamentation shade off so insensibly into the smooth and pohshed surface of the ordinary 

 Milioline shell (a specimen which is pitted or ribbed on one part of its surface being often 

 smooth on another, and this without any appearance of having been subjected to attrition), 

 that no use can be made of them as specific characters. Thus in the thickest-walled examples 



