132 FAMILY MILIOLIDA. 



where their walls are thinnest ; and such specimens, worn down to the line 1, 1, in Fig. XXIX, 



will present a series of large pits or openings between the rows of " junctural interspaces.'' This 



seems to be the condition of the form described by Defrance (xxix, torn, xxv, p. 287), under 



the name Larvaria reticidata ; and as there is here nothing 



Fig. xxix. inappropriate or deceptive in the trivial name, we retain it 



to distinguish the form of Badi/lopora now described. The 



f'^i^' '5^rirK close relationship between this type and the preceding is 



/ Ws>^\ T^^ ( evident.not merely from the general identity in the composition 



ckSS^^ ^-"-"—iS^SS" of each annulus, but also from the circumstance that the 



)C ^/f ?^°*^( average number of chambers which it contains is the same in 



aSSiSI — ' W«s«wf -^- reticulata as it is in I), annulus, and that the average 



Xf^y? ^^y diameter of the cylinder of the former is the same as that 



\^^~J- — - L_!-^^ of the rings of the latter. There is, in fact, every gradation 



between those disconnected rings, which are not unfrequently 

 Diaarrammatic vertical section of Z'fft'/y- r i i- i i it • ■ i ^i i <• 



loporaretic^.lata:-a,a,a,a,\.^r.A^:x^\ found shghtly adherent m pairs, and the compact column of 

 interspaces; 1, ], line of attrition. which the original annulation is but very imperfectly indi- 



cated on the surface. It is to be noticed in some of the most 

 compact specimens of this type (fig. 21) that the succession of the chambers in the adjacent 

 rings is not altogether regular, but that they in some degree alternate with each other, so as to 

 present a transition to the next variety ; and even when the annular divisions are well marked by 

 the rows of large "junctural interspaces,'' these divisions are sometimes considerably inflected. 



193. A modification of this simple type sometimes presents itself, in which the chambers 



are more than usually isolated from each other ; each being surrounded on all sides by its own 



proper wall, and "being connected with the adjacent chambers by projections of that wall ' 



(Plate X, fig. 25) ; between these projections are left "junctural interspaces" ij), h), which are 



sometimes passages of considerable size (fig. 28), and are sometimes narrowed to mere pores 



(fig. 26, 27). The apertures {a, a) of the chambers are here uniformly central, and are seated 



on nipple-shaped prominences (figs. 25, 26, 28). The external surface of the walls of the 



•chambers, in well-preserved specimens, is roughened by an irregular sculpture (fig. 27) ; a 



circumstance of interest with reference to the nature of the original surface in D. ci/Iinclracea. 



The piling of these chambers one upon another is not, as in D. reticulata, in distinct annuli ; 



for, although they usually form tolerably regular rows, the chambers in successive rows alternate 



with each other, those of one row lying in the hollows formed by the convexities of those in the 



rows above and below. — This seems to be the Microzoon figured and described by M. D'Archiac 



('Mem. Soc. Geol.,' 1850, tom. iii, p. 407, pi. viii, fig. 20) under the name Prattia glandulosa ; 



and as there can be no reason to regard it as anything else than a modification of the ordinary 



type of Bactyhpora (approaches to the alternating arrangement of the chambers being not 



unfrequently met with in B. reticulata^, it will here be distinguished as B. glandulosa. 



194. We now arrive at the type on which the genus Bactyhpora was founded, the 

 B. cylindracea of Lamarck ; which presents a very marked dissimilarity to all the preceding, 

 both in form, superficial aspect, and internal arrangement ; and yet it will be shown to be 

 not so far removed from them in the essentials of its structure, as to require being ranked in 



