EXPLANATION OF THE PLATES. 629 
Fig. 12. Embryonic disc, about 5 diam. Nanemys guttata ; 
from the oviduct, June 4, 1852. 
Fig. 13. The same as fig. 12; from the oviduct, June 3, 
1852. 
Fig. 14. Embryonic dise, 12 diam. ; from the oviduct, June 
8, 1852. Chrysemys picta. 
Fig..15. Embryonic disc, about 3 diam.; from the oviduct, 
May 29, 1854. Glyptemys insculpta. Fig. 15a, the same 
as fig. 15; the yolk, seen from above, nat. size. 
PLATE XI. 
[Fig. 1, 1a, 2, 3, 8a, 4, 4a, 4b, 5, 5b, 5c, from nature, by A. Sonrel; 
fig. 5a, 6, 6a, 7, 7a, 7b, 8, 9, 9a, 9b, 10, 10a, 10b, 10c, by 
H. J. Clark.] 
Tn all the figures, a is the region about the embryonic disc ; 
a‘, the cephalic hood; a’, the caudal hood; a’, a*, see Pl. 
9e, fig. 4, 4a, 4b, a®, at; a’, the end of the head; 
6, the primitive furrow; c, the area pellucida; d, the 
area yasculosa. 
Fig. 1. Embryo of Chelydra serpentina, 20 diam.; fig. 1a, 
the same as fig. 1, yolk and inner layer of albumen in 
profile, nat. size. Laid June 21; opened June 26, 1855. 
Fig. 2. Embryo of Chelydra serpentina, 20 diam. ; period 
of laying unknown ; opened June 16, 1854. 
Fig. 3. Ch. serpentina, 20 diam.; period of laying un- 
known, opened June 12, 1854 (in this figure, a should 
be d, as in fig. 2); fig. 3a, the same as fig. 3, yolk and 
inner layer of albumen in profile, nat. size. 
Fig. 4. Ch. serpentina, 20 diam.; period of laying un- 
known, opened June 12, 1854. Fig. 4a profile, and 4b 
from above, yolk and inner layer of albumen, nat. size. 
Fig. 5. Ch. serpentina, from above, fig. 5a from below; 20 
diam.; laid June 23, 1855, at 94 o'clock, A.m.; fig. 5 
opened June 26, 1855, at 4 p.M., fig. 5a opened about 
9 a.M., June 27, 1855; fig. 5b, profile of the whole egg 
of fig. 5 and 5a, nat. size; fig. 5c, the same as fig. 5b, 
seen as if cut through the middle to show the concave 
surface of the yolk, nat. size. 
Fig. 6. Malacoclemmys palustris, 18 diam.; laid and opened 
July 3d, 1855 ; fig. 6a, actual longitudinal section of fig. 
5; 25 diam. 
Fig. 7. Malacoclemmys palustris, from above; fig. 7a, the 
same as fig. 7, from below; 20 diam.; fig. 7b, longitudi- 
nal section of fig. 7 and 7a, 25 diam.; laid July °2, 
opened July 3, 1855. 
Fig. 8. Ozotheca odorata, from below; fig. 8a, anterior 
end of fig. 8, from above, 30 diam.; laid July 16, opened 
July 12, 1855. 


Fig. 9. Oz. odorata, from above ; fig. 9b, actual longitudi- 
nal section of fig. 9; fig. 9a, actual transverse section 
across the middle of fig. 9; 26 diam.; laid and opened 
July 4, 1855. 
Fig. 10. Malacoclemmys palustris, from above ; fig. 10a, from 
below; fig. 10b, actual longitudinal section ; fig. 10c, 
view of fig. 10 from front; 26 diam.; laid July 2, 
opened July 3, 1855. 
PLATE XII. 
[Figs. 2, 3, 8a, 8b, 4, 5, from nature, by A. Sonrel; the others by 
H. J. Clark.] 
In all the figures of this Plate, a designates the amnios; a’, 
the posterior bend of the cephalic hood; a’, the caudal 
hood ; a’, the point of disjunction of the subsidiary layer 
and of the germino-amniotic layer ; a°, the cephalic hood ; 
a‘, the basis of the cephalic hood; ec, the area pellucida; 
d, the area vasculosa; e, the spinal marrow; e', the up- 
ward folding borders of the brain; ¢*, the edge of the 
open medulla oblongata; ¢*, the point where the brain 
is closed over; ¢, the caudal portion of spinal marrow; 
J, vertebre ; f", the vertebral layer; g, the chorda dor- 
salis; h, the heart; 7, the vena afferens ; 7’, the vena ter- 
minalis; j, the branchial arteries; k, the eyes; /, the 
ears; m, the branchial fissures; 0, the abdominal aper- 
ture, and the basis of attachment to the amnios; p, the 
musculo-cutaneous layer. 
Fig. 1, from above; fig. 1a, from below; 25 diam. (In this 
ficure, c! should be e/.) Chelydra serpentina; laid 
June 12, opened June 28, 1855. 
Fig. 2, from above, 25 diam. Chelydra serpentina; laid 
June 12, opened June 26, 1855. 
Fig. 3, from below, on partially darkened background; fig. 
3a, the same as fig. 3, by transmitted light; fig. 3b, from 
above; 20 diam. Ch. serpentina; period of laying un- 
known, opened June 24, 1854. 
Fig. 4, from below, 22 diam. Ch. serpentina; period of lay- 
ing unknown, opened June 24, 1854. 
Fig. 5. Three quarters view from below, 22 diam. Ch. 
serpentina ; period of laying unknown, opened June 25, 
1854. 
Fig. 6. Right side and in profile, 24 diam. Nanemys gut- 
tata; period of laying unknown, opened July 28, 1852. 
Fig. 7, from below, 5 diam. Nanemys guttata; period of 
laying unknown, opened July 28, 1852. 
Fig. 8, from above and to the left, 24 diam. N. guttata ; 
laid July 18, opened July 30, 1852. 
