18 DE. CAEPENTEE'S EESEAECHES ON THE FOEAMINIFEEA. 



very prominent (Plate III. figs. 3, 4, 5), usually show this feature in the most decided 

 manner ; but it is occasionally presented also in no less a degree by those whose umbi- 

 licus is flat or even depressed. The most remarkable departure from the ordinary type 

 is seen in a small group of specimens in which the tubercles are not only extremely 

 large and prominent (Plate IV. fig. 6), but are distinguished by their opaque whiteness 

 (Plate V. fig. 12), which contrasts strongly with the semi-transparency ordinarily charac- 

 terizing these prominences. But even this character has no diagnostic value ; for a speci- 

 men which has the tubercles opaque in one part may have them semi-transparent in 

 another ; and as to the size of the tubercles, their degree of prominence, and the pro- 

 portion of the entire spire over the septa of which they occur, there is every degree of 

 variety. In one of my largest and flattest specimens, the central region is strongly 

 tuberculated, but the tubercles almost suddenly cease when the spire begins to open 

 out, and the septal bands are thenceforth as smooth as in the ordinary type. 



147. A less obvious but still very decided feature of individual difference, consists in 

 the presence or absence of papillary elevations between the septal bands. I have already 

 spoken (^[ 142) of the frequent existence of symmetrically arranged spots, sometimes 

 slightly depressed, but more commonly elevated, that are distinguished from the rest by 

 the semitransparency of their shell; these spots are sometimes considerably enlarged, 

 and their elevation increased, so that they become prominent papillae, closely resembling 

 the tubercles upon the septal bands. Their size and disposition vary considerably. 

 Sometimes they are small, numerous, and scattered without any definite arrangement 

 over the entire surface of the wall of the chamber, whilst in other cases they are con- 

 siderably larger, and form single, double, or even triple rows between the septal bands 

 (Plate V. fig. 10). Another remarkable variety of external aspect is produced by the 

 elevation of the general surface into rounded eminences closely abutting on one another 

 (like the pustules of the skin in a case of confluent small-pox), and distinguished from 

 the preceding by the absence of any peculiarity in the texture of the shell. That these 

 and other analogous variations of surface-marking have no value as differential characters, 

 is at once demonstrated, not merely by their gradational approximation in different indi- 

 viduals, but by the fact that they are presented in very different degrees on different 

 parts of the surface of the very same shell ; the chambers of one part of the spire being 

 strongly marked by certain of these peculiarities, whilst those of another may only 

 present indications of them, and those of a third may be perfectly smooth. 



148. The collection of Mr. CUMING, however, contains a group of forms which are at 

 once distinguished from the rest by their general physiognomy (Plate III. figs. 11, 12), 

 and which, when their characters are examined in detail, appear to be separated from 

 them by well-marked differences. Their aspect is much more lustrous, and their hue 

 much whiter, varied, however, by a tinge of green diffused in irregular patches ; the 

 spire does not in the largest specimens make above three turns, and it begins to open out 

 sooner than in the type already described; the septa are usually considerably more 

 convex anteriorly, and are also rather more distant from each other, so that the interval 

 between them is greater in proportion to the breadth of the spire, the shape of the 



