GENUS OPEllCULINA. 249 



the septa that bound them, so that the septal l)an(ls arc slightly furrowed ; whilst the 

 walls of the chambers arc sometimes a little depressed, so that the septal bands arc 

 prominent ; and such varieties may present themselves in different parts of one and the 

 same shell. Not unfrcquently the whole surface is seen to be marked by very minute 

 punctations ; luit more commonly they are larger and fewer in number, and are often 

 arranged in pretty regular lines parallel to the septal bands, — one, two, or three rows of such 

 punctations being seen on the wall of each chamber : these punctations, which often present 

 themselves abundantly on some parts of the surface, whilst they are entirely absent from 

 others, are found, when sufficiently magnified, to be spots of semi-transparent shell-substance 

 resembling that of the septal bands ; and, as in the case of these, their surface is sometimes 

 on the same plane with that of the general surface of the shell, sometimes a little elevated so 

 as to form papilkc, and sometimes a little depressed into minute fossae. Sometimes, instead of 

 a limited number of comparatively large and regularly arranged punctations, we find a vast 

 number of very minute papillae, scattered without order over the entire surface of the 

 chambers ; these, again, may be absent from some parts of a shell over other portions of 

 which they are abundantly distributed. There is commonly a large semitransparent tubercle 

 at the umbilicus, and smaller tubercles are often seen along the septal bands, especially of the 

 earlier whorls : not unfrcquently, however, the umbilicus is depressed instead of being elevated 

 into a tubercle, and the moniliform tubercles along the septal bands are wanting. 



434. The departures from this typical form, however, are very wide. A glance at any 

 considerable collection of specimens reveals to us an extraordinary variety not merely in size 

 but also in proportion ; and our attention is first attracted by a series which are not only 

 distinguished by a size greatly above the average — their long diameter reaching nearly4-l0ths 

 of an inch, — but also by the extraordinary flattening of the later convolutions, and the rapidity 

 with which the spire opens out. The approximation between the two lateral walls of the 

 chambers is here so close, that not only are the septal bands rendered very prominent by the 

 depression of the lateral surfaces between them, but even the outer marginal band stands up 

 as a ridge from which the walls of the chambers slope down. In fact, an examination of 

 this form leaves the observer impressed with sui-prise that any room can be left for the 

 animal, the segments of which must be extraordinarily attenuated, losing in thickness what 

 they gain in area. Now a careful comparison of this form with the ordinary type, not only 

 makes it obvious that the former difi'ers from the latter in no other particular than this attenua- 

 tion, which (as already pointed out in the case of Pcneroplis) is a common feature of the 

 later growths in Foraminifera, but also that the attenuation takes place in such difl'erent 

 degrees in different individuals, that any attempt to use it as a differential character is com- 

 pletely baffled by the continuous gradation of forms which is presented between the one 

 assumed as the typical and such as most widely depart from it in this particular. Among the 

 smaller Philippine specimens, on the other hand, a very different configuration is presented. 

 In those whose diameter docs not exceed 1-lOth.of an inch, the spire, instead of being flat, 

 or even somewhat hollowed, is often so highly arched between its inner and its outer margins 

 that the breadth of the septal plane is equal to its length or nearly so ; and a like turgidity, to 

 the degree represented in Plate XVII, fig. 1, sometimes shows itself in specimens of nearly 

 twice that dimension. This variety of conformation, however, being limited to shells whose 



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