GENUS CALCAEINA EXTEENAL CHAEACTEES. 
551 
margin of the central disk in such abundance, that very little of that margin is left free. 
The length of then’ spines, moreover, at different ages, varies pretty constantly with the 
diameter of the disk, the average proportion being about two-thirds ; though we occa- 
sionally meet with specimens in which the disk is unusually large and the length of the 
spines does not equal more than half its diameter, and others in which the disk is 
unusually small and the length of the spines is equal to its whole width. In the 
Mediterranean Calcarince (Fig. III.), on the other hand, I have seldom met with more 
than nine spines ; and any excess beyond that number is only presented by specimens 
in which the disk is very large, so that wide intervals present themselves along its 
margiu between the bases of the spines (Plate XIX. fig. 2). Their spines are nearly always 
simply clavate in form, any tendency to bifurcation or trifurcation at their extremities 
being rare ; and they show but little disposition to increase in length with the enlarge- 
ment of the central disk, being often not only relatively but even absolutely shorter in 
old specimens; as if the spines had entirely ceased to grow, and the disk had (as it 
were) included their basal portions within itself. In some instances, indeed, they 
scarcely show themselves enough to attract attention ; being little more than tubercular 
projections from the margin of the disk (Fig. III. h). Notwithstanding, however, this 
strongly marked difference in general physiognomy, it becomes obvious, on the com- 
parison of a sufficient number of individuals, that no line of specific distinction can be 
fairly drawn on such a basis between the Philippine and the Mediterranean forms; 
since among the Philippine we meet with not a few specimens, in which the spines are 
as few and simple as they are in the great bulk of the Mediterranean (Fig. III. b, c) ; 
and specimens not unfrequently present themselves among the Mediterranean (Plate XIX. 
fig. 2), in which there is not merely an addition to the ordinary number of the spines, but 
a manifest disposition in many of them to subdivide near their extremities, thus showing 
an ob\ious approximation to the Philippine type. Although the spines usually radiate 
nearly in the equatorial plane, yet it becomes obvious, when their connexion with the 
central disk is examined, that they originate at different levels (Fig. III. e, f) ; this will 
presently be found to depend on the fact that the form of the spire is not nautiloid but 
turbinoid. Besides the ordinary radiating spines, an extraordinary growth of short pointed 
spines is sometimes seen, either partially or completely covering one or both surfaces of 
the central disk (Fig. II. g) ; and examples occasionally present themselves (Fig. I. a), in 
which the development of these seems to have altogether superseded that of the ordinary 
radiating spines. 
198. It is remarkable that among the very young specimens of this type, a yet greater 
variety shows itself than among those further advanced in life. In Plate XIX. figs. 5, 
6, and 7, are shown what may be considered the ordinary or normal aspect of the very 
young Calcarina', whilst in figs. 8-II, and Plate XX. fig. 6, we have representations 
(under higher magnifying powers) of examples of what may be termed the hispid con- 
dition, which so frequently presents itself in small Calcarinm as to give rise to a question 
whether they should not be made to constitute a distinct species. I have satisfied 
