16 DB, CAEPENTEE'S EESEAECHES ON THE FOEAMINTFEEA. 



regularly arranged punctations, we find a vast number of very minute papillae, scattered 

 without order over the entire surface of the chambers (fig. 6) ; 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 : 

 the umbilical and the septal tubercles are well seen in Plate III. fig. 6, and (less charac- 

 teristically) in several other figures of the same Plate; and the septal tubercles are 

 shown on a much larger scale in Plate V. fig. 11. Not unfrequently, however, the 

 umbilicus is depressed, instead of being elevated into a tubercle ; and the moniliform 

 tubercles along the septal bands are wanting. 



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

 any considerable aggregation of specimens reveals to us an extraordinary variety of size 

 and shape ; and our attention is specially attracted by a series of which an example is 

 represented in Plate III. fig. 9, which are not merely distinguished by a size greatly 

 above the average their long diameter reaching nearly -4 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 outer surface 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 exami- 

 nation of this form leaves the observer impressed with surprise 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 differs from the latter in no 

 other particular than this attenuation, which (as already pointed out in the cases of 

 Heterostegina and Peneroplis) is a common feature of the later growths in Foraminifera, 

 but also that the attenuation takes place in such different degrees in different individuals, 

 that any attempt to use it as a differential character is completely baffled by the con- 

 tinuous gradation of forms that is presented, between the one which has been assumed 

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



144. The collection of Mr. CUMING also includes, however, a considerable proportion 

 of comparatively small specimens, ranging from -08 to -20 inch in diameter, which pre- 

 sent a very different configuration. In the smallest of these, represented in Plate III. 

 fig. 1, the spire, instead of being flat or even somewhat hollowed, is arched from its 

 inner to its outer margin, so that the breadth of the septal plane is equal to its length, 

 or nearly so ; and the like is seen in the somewhat larger specimens of which fig. 2 is an 

 example. This variety of conformation, however, being limited to shells whose earlier 

 period of growth is evinced by their smaller number of convolutions and of chambers, 

 and being seen, moreover, in the earlier whorls of those which afterwards present the 

 greatest flattening, may safely, I think, be regarded as a character of age. It will be 

 recollected that the young of the flattened Peneroplis more resembles Dendritina in the 

 comparative turgidity of its spire ; but I do not find that Operculina ever continues long 



