630 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Rhynchotrema inaequivalvis Castelnau, WINCHELL and SCHUCHERT, Geol. Minnesota, vol. 3, 
pl. 34, figs. 24, 25, 1895. 
Types.—Figured hypotypes: 11721 Ia-c. 
Horizon and locality—Trenton formation in Kentucky: Danville, Boyle 
County; Burgin, Mercer County; Paris, Bourbon County; and Curdsville, Da- 
viess County. 
RHYNCHOTREMA WISCONSINENSE Fenton and Fenton 
Plate 128, H, figures 40-48; plate 138, G, figures 43-45 
Rhynchotrema wisconsinense FENTON and FENTON, Proc. Iowa Acad. Sci. for 1922, vol. 209, 
p. 71, pl. 1, figs. 6-8, 1924. 
Rhynchotrema inaequivalvis Castelnau (part), WINCHELL and ScHucHERT, Geol. Minnesota, 
vol. 3, pl. 34, figs. 13, 14, 1895. 
Types.—Figured hypotypes: 24843a,b, 1172I0a. 
Horizon and locality—Decorah formation (Ion member) in Minnesota and 
Wisconsin. 
Genus ROSTRICELLULA Ulrich and Cooper, 1942 
Rostricellula UtricuH and Cooper, Journ. Paleont., vol. 16, No. 5, p. 625, 1942. 
Shell rhynchonelliform, generally subtriangular to subpentagonal in outline, 
more rarely transversely elliptical, Anterior commissure uniplicate. Pedicle 
valve with pointed and generally incurved beak ; delthyrium open or partially re- 
stricted by rudimentary deltidial plates. Interarea narrow, almost obsolete. 
Pedicle interior with strong dental plates separated from the sides of the valve 
by narrow umbonal cavities. Teeth small, curved. Delthyrial cavity deep, oc- 
cupied wholly by the scar of the pedicle attachment; muscle field situated an- 
terior to the delthyrial cavity, like Rhynchotrema in pattern. 
Brachial interior with divided hinge plate united to median septum by short 
supporting plates that form a small chamber or cruralium beneath the beak. 
Brachial processes long and slender, curved. Median septum strong, elevated, 
reaching to middle of valve or beyond. Adductor impressions located on each 
side of the septum in the posterior half of the shell. Cardinal process absent. 
Genotype—Rostricellula rostrata Ulrich and Cooper, new species. Journ. 
Paleont., vol. 16, No. 5, p. 626, pl. go, figs. 24, 28, 29, 32, 37, 1942. 
Discussion—This genus differs from Rhynchotrema by absence of a cardinal 
process in the brachial valve and nonimbricate ornamentation. 
ROSTRICELLULA ACUTIPLICATA Cooper, new species 
Plate 133, F, figures 36-41; plate 138, D, figures 25-38 
Shell of about medium size for the genus, wider than long with a somewhat 
rectangular outline in the old adult but triangular in young adults. Apical angle 
about 105°. Sides rounded; anterior margin truncated. Widest slightly an- 
terior to the middle. Fold marked by 3 to 5 costae, the sulcus by 2 to 4, and the 
flanks by 7 to 9. Surface finely filate and papillose. 
