I2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 134 
and roughly T-shaped in ventral aspect. Sutures: Slightly depressed 
and markedly curved on the dorsal surface in the last whorls; less 
depressed and less curved in earlier whorls. Ventrally, depressed, 
especially toward the umbilicus. Apertures: In the last whorl situ- 
ated at the umbilical ends of the ventral lobes of the chambers. They 
point into the umbilicus under shelflike lips and may be directed 
toward the center of the umbilicus or backward toward the earlier 
chambers of the whorl. Where the last chamber is highly developed, 
the lip on its umbilical projection may obscure the earlier apertures. 
Many specimens show a fusion of the umbilical projections of the 
chambers, obscuring most if not all of the apertures. Size: Hypotype 
of figure I, maximum diameter 0.53 mm., approximate thickness 
0.16 mm. Hypotype of figure 2, maximum diameter 0.35 mm., ap- 
proximate thickness 0.13 mm. 
Locality—Hypotypes (U.S.N.M. Nos. P5109a,b) from sample 
Bo. 262. Ortoire River, east coast, Trinidad. Hypotype (U.S.N.M. 
No. P5110) from sample Bo. 261, Ortoire River, east coast, Trinidad. 
Hypotype (U.S.N.M. No. P5112) from sample J.S. 135, Ortoire 
River, east coast, Trinidad. 
Distribution.—This species is especially characteristic of the brack- 
ish-water sections of the Trinidad rivers; it is found less commonly 
in the swamps. 
Remarks.—The true character of the apertures in this species was 
not described by Cushman and Bronnimann. The apertural features 
noted in this emended diagnosis make is necessary to remove this 
species from the genus Trochammina Parker and Jones, 1859. In 
Trochammina, only the last aperture opens to the exterior; each 
earlier aperture is concealed by the addition of the next chamber. 
Genus ARENOPARRELLA Andersen, 1951, emend. Andersen, 1951 
ARENOPARRELLA MEXICANA (Kornfeld) emend. Andersen 
PLATE 4, FIGURE 5 
Trochammina inflata (Montagu) var. mexicana KorNFELD, Contr. Stanford 
Univ. Geol. Dept., vol. 1, p. 86, pl. 13, figs. 5a-c, 1931. 
Arenoparrella mexicana (Kornfeld) ANpbERSEN, Journ. Paleontol., vol. 25, 
No. I, p. 31, figs. Ia-c, 1951. ANDERSEN, Contr. Cushman Found. Foram. Res., 
vol. 2, pt. 3, p. 96, pl. 11, figs. 4a-c, 1951. 
Diagnosis —Shape of test: Trochospiral, involute ventrally with a 
smooth or very slightly lobate equatorial periphery ; dorsal side slightly 
convex; ventral side with a small, depressed, closed umbilicus. Axial 
periphery rounded. Wall: Fine sand grains set in abundant cement ; 
