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ME. W. K. PAEKEE AND PEOFESSOE T. E. JONES ON SOME 
same rapid increase of size, with the same neat convergence of the umbilical lobes ; the 
lines between them, however, being usually straighten The conditions of the umbilicus 
resemble those of the typical group ; but the contracted form of the shell, in certain 
varieties, raises up the umbilical portions of the chambers into the apex of a cone, the 
base of which is the neat and almost flat spiral surface. 
The members of this group, all of which are mutual companions, are obtained from 
abyssal depths, 100 to 2700 fathoms. 
Fourth Group, characterized by P. Schreibersii. — These shells have more numerous 
chambers than we find in the foregoing groups, nor do they enlarge with age so rapidly. 
The lower surface shows but few chambers (5-11), in contrast with those seen above 
(15-30) ; whilst in groups Nos. 1-3, all except the four or five earliest chambers are seen 
on the umbilical as well as on the spiral surface, on account of the spire being subdis- 
coidal, whilst in P. Schreibersii and its allies the spire is helical or subturreted. There 
is also a greater tendency to limbation (exogenous shell-growth on the septal lines and 
the margin), especially about the umbilicus, where a knob, a group of granules, or a 
star-like ornament is not unusual ; hence this may be termed the “ stellar ” group. 
These, moderately deep-sea forms for the most part, have often the thickest shells of any 
among the subtypes, especially P. Schreibersii itself, as found in the muds of the Gulf 
of Suez at about 40 fathoms. This group has a very extensive bathymetrical range. 
Fifth Group, with P. elegans as the leading form. — This is closely allied to the last 
group in its general features, and may be said to represent a further development of its 
peculiarities. We have here a series of neat, compact, more or less biconvex, and for 
the most part limbate Pulvinulince. The limbation is less constant on the upper (spiral) 
than on the lower surface, on which latter a symmetrical wheel-like ornament is often 
found, imitating such as occurs on some nautiloid Cristellarice. On the upper surface 
the limbation is sometimes strongly developed, both on the septal lines and the margin, 
and in some cases (P. D'Orbignii , Rcemer, and P. ornata , Roemer) masks the spire 
altogether. On the other hand the limbation may be but slight ; and in P. Cordieriana , 
excepting as regards the umbilical boss, it is nearly obsolete. Some subvarieties of P. 
elegans itself appear with little exogenous or limbate ornament. 
In this group the shell is polished to the utmost ; and in the same gatherings from 
very deep water P. Menardii will be in its roughest condition and P. elegans will be 
highly enamelled and glistening. It is always neat and nautiloid. The group ranges 
from 70 to 1000 fathoms. 
