486 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
ones of M. globosa. In general M. tumida is more strongly costellate than the 
general run of M. globosa, but it is suggestive of the more strongly costellate 
ones called M. superba by Dr. Butts. However, the pedicle valve of the Hogskin 
species is more tumid than that of M. globosa. 
MIMELLA ULRICHI Cooper, new species 
Plate 87, A, figures 1-5 
Shell small for the genus, transversely rectangular in outline; sides rounded; 
cardinal extremities obtusely rounded ; anterior margin emarginate medially ; an- 
terior commissure gently and broadly sulcate. Multicostellate, costellae narrowly 
rounded, closely crowded, increasing by bifurcation, often fasciculate. 
Pedicle valve evenly and gently convex in lateral profile; broadly convex in 
anterior profile with the median region rounded and long, moderate slopes to the 
margins. Umbonal region swollen, the swelling continuing anteriorly but increas- 
ingly indistinct to the front margin and thus serving as a poorly defined fold. 
Flanks gently convex and sloping moderately to the margins. Interarea curved, 
nearly catacline ; beak gently incurved. 
Brachial valve having less depth than the pedicle valve, gently but evenly con- 
vex in lateral profile. Anterior profile broadly convex but depressed slightly in 
the median region and with moderately long and moderately steep lateral slopes. 
Umbo sulcate ; sulcus shallow throughout its length, originating at the beak and 
extending to the front margin. Flanks bounding sulcus gently swollen; lateral 
slopes moderately short. Interarea short, anacline. 
Measurements in mm.—Holotype, length 7.9, brachial length 7.2, width 10.7, 
hinge width 9.4, thickness 4.8. 
Types.—Holotype: 110805. 
Horizon and locality—Crown Point formation in New York: At Sloop Bay, 
Valcour Island, Lake Champlain, Plattsburg (15’) Quadrangle. 
Discussion.—This little species is characterized by its transversely rectangu- 
lar outline, strongly sulcate brachial valve, wide hinge, and fine costellae. It 
occurs with M. nucleoidea but is readily distinguished by its greater width. 
MIMELLA VALCOURENSIS Cooper, new species 
Plate 85, C, figures 27-32 
Shell of about medium size for the genus; wider than long and with a some- 
what rectangular outline; depth of valves subequal; greatest width anterior to 
the middle; lateral margins sloping obliquely anteriorly to the narrowly rounded 
anterolateral extremities. Anterior margin slightly emarginate; anterior com- 
missure broadly and gently uniplicate. Surface multicostellate, costellae broad, 
crowded, 8 or 9 in the space of 5 mm. at the anterior margin of the flanks, nar- 
rower and more crowded in the midregion. 
Pedicle valve having unequal convexity, the most convex part in the posterior 
half, the anterior half sloping steeply toward the brachial valve; anterior profile 
