GENUS CALCARINA. 219 



381. Returning, now, to the external aspect of the fully-developed Calcarina, 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 XIV, fig. 1). Tiiese 

 are sometimes large and prominent, and present the semi-transparent appearance which is 

 common among the like tubercles of Operculina (IT 436) ; more commonly, however, they are 

 less conspicuous either as to size, prominence, or distinctive aspect ; and sometimes they are 

 almost or altogether wanting (fig. 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 surface corresponding to tlieir usual situation. 

 For whilst the exterior of the disk is marked, more or less conspicuously, with minute 

 punctations (fig. 8), 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 

 punctations being uniformly distributed over the surface, which is in that case always the 

 one nearest the apex of the spire. Tiie surface of the spines is marked, more or less 

 conspicuously, by a longitudinal furrowing (fig. 8), not unlike that of the "marginal cord" of 

 Operculina (^ 444). The furrows maintain a general parallelism, but there are frequent 

 inosculations between them ; and punctations marking the orifices of deeper canals are 

 often to be noticed at the bottom of the furrows. On one of the surfaces of the disk the 

 indication of a sj)ire is more or less distinctly observable (Plate XIV, fig. 1) ; also 

 (Fig. XXXIV, B, Fig. XXXV, 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, are extremely thin 

 (Plate XIV, fig. 8, b, b), 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 Fichtel and Moll, and appa- 

 rently by D'Orbigny also, for the true aperture of the shell, which, as will presently appear, is 

 of an entirely different character, and is not easily to be distinguished. The prominent surface 

 of the walls of the conspicuous chambers of the newest whorl is covered with punctations 

 resembling those of the general surface of the disk ; but they are more minute and more 

 closely set together, and they are distributed with great uniformity, no unpunctated spaces 

 being anywhere visible. 



382. Internal Structure — When the internal structure of this organism is examined by 

 means of thin sections taken in different directions, the apj^arent anomalies of its conformation 

 are found to be dependent simply upon the extraordinary development of its " supplemental 

 skeleton ;" its general plan of structure being much simpler than the peculiarities of its aspect 

 would seem to indicate. The spire, as laid open by vertical section (Plate XIV, fig. 3), is 

 turbinoid ; consisting usually of about five whorls {a, a^, a~, c?, a^), that start as usual from 

 a central cell, and progressively increase in size ; each whorl is applied merely to the 

 surface of the preceding, and does not invest it in any degree, the chambers being altogether 

 destitute of alar prolongations. The aspect of the spire as seen in equatorial section is 



