Late Cenozoic Ostracodes — Holden 
13 
teriorly acuminate; greatest height at anterior 
part of dorsal margin; dorsoposterior with con- 
spicuous dorsally humped caudal process (ter- 
minating with spine in young) ; dorsoanterior 
slightly concave, sloping at about 30° ; ventral 
margin gently convex, continuous with straight 
to slightly convex ventroposterior ; ventropos- 
terior serrate in young, some adults with occa- 
sional denticles ; ventroanterior broadly and 
gently rounded, subtruncate; surface smooth. 
In dorsal view: carapace posteriorly acuminate; 
greatest width, like height, just anterior to mid- 
length ; trace of hinge line with left valve 
broadly arched over right valve. 
Duplicature not broad ; vestibules large ; other 
internal features obscured. 
dimensions: See Table 5. 
distribution: As fossils from T-l (2 valves; 
13 entire), T-2 (6 valves), T-4 (1 valve; 1 
entire), T-ll (5 valves; 1 entire), T-12 (28 
valves; 10 entire), and AR (1 valve). 
discussion: Other than sexual dimorphism 
with taller males, little variation occurs in the 
species. Shape and inflation, characteristic of 
mature specimens, is also consistent in the young 
to at least the fourth-from-last instar. 
Bairdia gerda Benson and Coleman, 1963, 
from the west coast of Florida, is quite similar 
to the present species. B. gerda differs from B. 
ritugerda only by the lack of the dorsally 
humped caudal process, the presence of a 
straighter venter, and by a more pointed dor- 
sum. 
Bairdia crosskeiana Brady, 1866 of Brady 
1880 (a misidentification?) is closely related to 
B. ritugerda, as attested by the presence of a 
well-developed terminal spine in the young, a 
humped caudal process, and general shape 
(though much lower than the former species). 
Specimens of B. crosskeiana of Brady, 1880 
found at T-l 3 are illustrated for comparative 
purposes (Fig. 6 h-l). 
Bairdia attenuata Brady, 1880 
Figs. 7 a—d 
Bairdia attenuata Brady, 1880. Rept. Voy- 
age Challenger, Zool. 1, pt. 3, p. 59, pi. 11, 
figs. 3 a-e. 
Bairdia attenuata Brady. Egger, J. G., 1901, 
Abh. Math.-Phys. Cl. koninkl Bayer. Akad. 
Wiss. 21, no. 2, p. 425, pi. 2, figs. 9, 12. 
diagnosis : Posterior and anterior sharply up- 
turned, especially pronounced in left valves; 
terminally compressed carapace; high, rounded 
dorsum. 
description: In lateral view: surface faintly 
pitted ; dorsal margin arched ; dorsoanterior and 
dorsoposterior conspicuously concave; anterior 
margin slightly convex; ventroposterior broadly 
rounded ; ventroanterior broadly rounded in 
lower part, tightly rounded in upper part. In 
dorsal view: carapace compressed, diamond 
shaped; greatest width medially; ends evenly, 
sharply acuminate; males taller than females. 
Adductor muscle scar pattern of about seven 
small scars encircling a single larger scar ; 
antennal or mandibular scars not observed. 
Posterior vestibule shallow, anterior vestibule 
bilobed, shallow; radial pore canals abundant, 
simple; normal pores minute, dense. 
dimensions: 
PLESIOTYPE 
LENGTH 
WIDTH 
HEIGHT 
usnm 648737 
(left valve $ ) S-23 
1.05 
0.33 
0.67 
SDNH 1037 
(entire $ ) AR 
1.12 
0.50 
0.70 
usnm 648738 
(left valve $ ) T-12 
1.05 
0.32 
0.63 
TABLE 5 
Dimensions of Bairdia ritugerda n. sp. 
SPECIMEN 
LENGTH 
WIDTH 
HEIGHT 
Holotype usnm 648731 (left valve $ ) T-12 
1.17 
0.34 
0.68 
Paratype usnm 648732 (right valve 8 ) T-12 
1.08 
0.24 
0.57 
Paratype sdnh 1034 (left valve 8 ) T-12 
1.05 
0.34 
0.67 
Paratype sdnh 1035 (penultimate, left valve) T-12 
0.88 
0.24 
0.50 
Paratype usnm 648733 (third from last, left valve) T-12 
0.69 
0.19 
0.40 
Paratype sdnh 1036 (fourth from last, left valve) T-12 
0.53 
0.14 
0.30 
Paratype usnm 648734 (right valve) T-12 
1.00 
0.25 
0.55 
