GENUS ORBITOLTTES: — EXPLANATION OF PLATES. 
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Fig. 6. Nucleus and first two annular zones of another disk, showing a deficiency in 
the connexions of the first annular zone with the circumambient segment hh, 
for about a third of the circumference of the latter, between the points 
cc : — 84 diam. 
Fig. 7- Portion of one of the surfaces of an animal of complex type (as in fig. 4) : — 
aa, aa, rows of superficial cells, connected at their two extremities with 
the annular bands bh, hb: — 150 diam. 
Fig. 8. Portion of fig. 1, enlarged, to show the ordinary mode in which the segments 
of each zone are connected by peduncles with the annular hand of the pre- 
ceding zone, so as to alternate with its segments ; showing also the 
occasional interpolation of additional segments, a, a, whose peduncles come 
off from the segments of the preceding zone: — 90 diam. 
Fig. 9. Portion of a section of the shelly disk enlarged, to show the corresponding 
appearances it presents ; each cell being ordinarily connected by a radial 
passage with the annular canal of the preceding zone, and thus with the 
two cells alternating with itself; but cells a, a, being sometimes interpo- 
lated, which open directly into the cells of the preceding zone : — 90 diam. 
Fig. 10. Central and circumambient segments {a and hh) of a large disk, showing 
the origin of the segments of the first annular zone, c, c, from less than half 
the circumference of the nucleus: — 84 diam. 
Fig. 11. Peculiar bodies (ova?) found in the substance of the sarcode in different 
parts, showing successive stages, a, b, c, d, e, f, of binary subdivision ; 
g, other bodies of somewhat larger size, found in one of the superficial cells 
of a vertical section : — 130 diam. 
Fig. 12. Central portion of fig. 1, enlarged to the same scale as figs. 5, 6, 10 ; show- 
ing the central segment a, the circumambient segment hh, and the origin 
of the first annular zpne in three peduncles proceeding from the end of the 
latter: — 84 diam. 
Fig. 13. Central portion of another disk, showing the origin of the first annular zone 
by eight peduncles from the circumambient cell: — 84 diam. 
PLATE V. 
Structure of the Calcareous Disks of Orbitolite. 
Fig. 1. Ideal Representation of a Disk of the Simple Type, the. details of the different 
parts made-up from actual specimens ; showing the natural surface, with 
the markings of the cells ; the natural margin, with the single row of pores 
between the protuberances of the cells ; — a portion of the interior, as dis- 
played by a horizontal section, showing the central cell a, the circumam- 
bient cell h, h, the concentric zones of cells c, c, with the annular passages 
which connect together the cells of the same zone, and the radiating passages 
2 H 2 
