44 
PACIFIC SCIENCE, Vol. XXI, January 1967 
median ridge; anterolateral and posterior areas 
compressed; valves unequal, posterodorsal rib 
juncture more posterior in right valve. 
Hinge holamphidont: posterior tooth of 
right valve rounded, heavy; anterior tooth and 
postjacent socket large, median groove smooth. 
Radial pore canals abundant, muscle scars and 
other internal features obliterated. 
DIMENSIONS : 
SPECIMEN 
LENGTH 
WIDTH 
HEIGHT 
Holotype usnm 648756 
(entire $ ) T-l 2 
0.58 
0.19 
0.28 
Paratype sdnh 1063 
(entire $ ) T-12 
0.53 
0.17 
0.28 
Paratype usnm 648757 
(left valve $ ) T-12 
0.57 
0.12 
0.28 
distribution: As 
fossils 
from T-l 2 (7 
valves; 3 entire). 
discussion: Penultimate instars of N. terryi 
are densely pitted (a finer pattern than on N. 
reticulata) and have a rneiodont hinge. 
Named in honor of D. Terry, of North 
American Aviation Corporation, who collected 
samples T-l through T-13. 
Family xestoleberididae Sars, 1928 
Genus Xestoleheris Sars, 1866 
Xestoleheris nana Brady, 1880 
Figs. 34 a-d 
Xestoleheris nana Brady, 1880. Rept. Voyage 
Challenger, Zool. 1, pt. 3, p. 126, pi. 31, figs. 
3 a—c. 
diagnosis : Greatly inflated carapace ; flat 
venter; low, pointed anterior. 
description: Carapace almost oval in dorsal 
view: rounded posteriorly, slightly acuminate 
anteriorly. In lateral view: ventral margin long, 
straight; dorsal margin broadly rounded, slop- 
ing down anteriorly ; left valve overlapping 
right valve around entire margin ; surface 
smooth. 
Hinge antimerodont : right valve with arcuate 
crenulate anterior bar, deep arcuate crenulate 
median furrow medially covered by thick dorsal 
ledge, and short, straight, heavily notched, pos- 
teriorly extending rear element. 
Adductor muscle scar pattern large, of four 
irregular scars in vertical row; V-shaped anten- 
Fig. 34. Xestoleheris nana Brady, 1880. a-b, Plesiotype usnm 648767 ; a, right valve view of entire fe- 
male(?) carapace showing overlap of left valve; b , dorsal view, c-d, Plesiotype sdnh 1064; c, internal view 
of female (?) right valve; d, dorsal view. 
