552 
DE. CAEPEXTEE’S EESEAECHES OX THE EOEA^imTEEA. 
myself, however, by the comparison of a large number of specimens, that so continuous 
a gradation presents itself between the smoothest and the most hispid specimens, as 
to render the attempt to separate them specifically altogether futile ; and Mr. W. K. 
Parkee, who has examined a yet larger number of specimens, fully confirms this 
conclusion. Moreover the internal structure of these hispid specimens, as shown in 
horizontal section (Plate XX. fig. 8), shows no departure whatever from the ordinary 
type. 
199. Returning, now, to the external aspect of the fully-developed Calcaiina, we have 
to notice that each surface of the disk is very commonly elevated, especially in its central 
portion, into rounded tubercles, more or less closely set together (Plate XIX. figs. 3, 4). 
These are sometimes large and prominent, and present the semitransparent appearance 
which is common among the like tubercles of Operciilina (^ 146) ; more commonly, 
however, they are less conspicuous either as to size, prominence, or distinctive aspect ; 
and sometimes they are almost or altogether wanting (figs. 1, 2). Yet it is seldom, if 
ever, that they are absent from both surfaces of the disk ; and it is more common to find 
them deficient on the surface nearest to the apex of the spire, than on that on which its 
last-formed chambers are visible. And even when no prominent tubercles are present, a 
distinction may be generally made out by careful examination in the parts of the smiace 
corresponding to their usual situation. For whilst the exterior of the disk is marked, 
more or less conspicuously, with minute punctations (figs. 1, 3, 4), these are not to be 
seen on its tuberculated prominences ; and the like deficiency is generally to be noted 
in circular spots of the surface, even when it is not raised into tubercles. Occasionally, 
though rarely, not even this mark of differentiation is seen, the pmictations being 
uniformly distributed over the surface, which is in that case always the one nearest the 
apex of the spire. 
200. The surface of the spines is marked, more or less conspicuously, by a longitu- 
dinal furrowing (figs. 1, 3, 4), not unlike that of the “ marginal cord ” of Operculum 
(^ 156). The furrows maintain a general parallelism, but there are frequent inoscu- 
lations between them ; and punctations marking the orifices of deeper canals are often 
to be noticed at the bottom of the furrows. 
201. One important feature of the external aspect of the disk has yet to be mentioned ; 
namely, the indication of a spire^ which more or less distinctly presents itself on one of 
its surfaces (Fig. II. b. Fig. III. d, g, h). This indication is sometimes limited to two or 
three chambers ; but more commonly about half a turn may be distinguished, the spire 
becoming absorbed (as it were) into the solid mass of the disk, as we trace it backwards. 
The walls of the last-formed chambers, where entirely disengaged from the disk, ai'e 
extremely thin (Plate XIX. fig. 4), so that it is rare to find them perfect ; and an opening 
formed by the fracture of the wall of the newest chamber has been mistaken by Mi\I. 
Fichtel and Moll, and apparently by M. d’Orbigny also, for the true aperture of the 
shell, which, as will presently appear, is of an entirely different character, and not easily 
to be distinguished. The prominent surface of the walls of the conspicuous chambers 
