572 DE. W. B. CARPENTER ON ORBITOLITES TENUISSIMA. 



the annuli external to them ; b, b, b, annular galleries traversing the septa 



between the chamberlets. At a, a, are seen the openings through which the 



sarcodic cords that occupy the annular galleries send radial extensions into 



the chamberlets of the succeeding annuli. Magnified 64 diameters. 

 Fig. 4. Internal aspect of a small portion of an annulus detached by fracture ; showing 



the entrances to the chamberlets of that annulus through the septal plane. 



Magnified 64 diameters. 

 Fig. 5. External or peripheral aspect of a portion of a marginal annulus, showing the 



passages through its septal plane, as marginal pores elongated in the plane 



of the disk. Magnified 64 diameters. 

 Fig. 6. Portion of a disk, whose remainder, with the " nucleus," has been lost by 



injury previously to the formation of the last two annuli, which have 



extended themselves along the fractured margin, and into the nuclear space. 



Magnified 15 diameters. 

 Fig. 7. Incipient production of an entirely new disk, with regularly concentric annuli, 



from a fragment of the peripheral portion of an old one. Magnified 15 



diameters. 



PLATE 38. 



Structure of Sarcodic Body and Calcareous Disk of Orbitolites tenuissima. 



Fig. 1. Sarcodic body of the central portion of the disk; showing the primordial seg- 

 ment giving off the spiroloculine coil, the sixth turn of which, a, begins to 

 open out into a peneropline form, afterwards becoming divided into rows of 

 orbiculine sub-segments, which are connected together laterally by the con- 

 tinuity of the sarcodic body through the gallery at the outer end of each 

 row, and radially by the stolon-processes that pass through the septal pas- 

 sages, from the gallery of the inner row into the chamberlets of the outer. 

 Nuclear (?) corpuscles are seen irregularly distributed through the sarcodic 

 substance. Magnified 75 diameters. 



Fig. 2. Nuclear (?) bodies, as seen under a power of 450 diameters. 



Fig. 3. Section of first-formed portion of the disk, laying open the primordial chamber, 

 a, and the spiroloculine chambers, partially divided as at b, which coil round 

 it. Magnified 125 diameters. 



Fig. 4. Portion of the sarcodic body shown in fig. 1, enlarged to 125 diameters, to 

 show the distribution of the nuclear (?) corpuscles : a, expanded extremity 

 of the last spiroloculine coil ; b, b, b', b', portions of preceding coils, crowded 

 with nuclear (?) corpuscles ; c, orbiculine sub-segment, with five corpuscles ; 

 d, d, d, d, orbiculine sub-segments, each with one or with two corpuscles. 



Fig. 5. Central portion of the calcareous disk, as seen by transmitted light ; a, ex- 

 panded chamber formed by the termination of the spiroloculine coil, and 



