422 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Plaesiomys platys (Billings) RayMonp, Ann. Carnegie Mus., vol. 7, p. 238, pl. 35, figs. 13-14, 
IQIl. 
Multicostella platys (Billings) ScHucHERT and Cooper, Mem. Peabody Mus. Nat. Hist., 
vol. 4, pt. 1, p. 98, 1932. 
Like all species of Multicostella this one is also very variable in size and cer- 
tain of the details of the surface. The type specimen (G.S.C. 1034) which is pre- 
served in the Geological Survey of Canada collection is a fairly large specimen 
but is poorly preserved. Much of the exterior has been stripped from the shell, 
making it impossible to determine the details of the costellae exactly. The con- 
vexity of both valves is low and at the front of the pedicle valve the specimen is 
depressed to form a broad and shallow sulcus. The sulcus of the brachial valve is 
shallow and narrow and extends about to the middle of the valve. At the front of 
the brachial valve a low swelling corresponds to the sulcus of the pedicle valve. 
Some specimens show a clearly defined sulcus in the brachial valve extending 
from the beak to the anterior margin. Ten costellae may be counted in a distance 
of 5 mm. at the front margin of the holotype. Inasmuch as this specimen is much 
exfoliated, it is possible that the finest costellae of the latest generation are lost 
and cannot be counted. The holotype is 18.5 mm. long, 21 mm. wide, and 5.5 mm. 
thick. Specimens preserving the exterior show the costellae to be narrow, ele- 
vated, and bundled with ones of various sizes in several generations. 
Types.—Holotype: G.S.C. 1034; figured hypotype: Carnegie Mus. 5467 (on 
same slab with Valcourea strophomenoides). 
Horizon and locality—Common in the Crown Point formation in New York: 
Crown Point, Port Henry (15’) Quadrangle; Plattsburg and Valcour Island, 
Plattsburg (15’) Quadrangle ; Chazy, Rouses Point (15’) Quadrangle. 
Same formation in Vermont: On Isle La Motte, Rouses Point (15’) Quad- 
rangle. 
St. Martin formation, Island of Montreal, Quebec, Canada. 
Discussion.—This species is most like M. saffordi but is in general smaller in 
size and somewhat more quadrate. It is also suggestive of M. plena from which 
it differs in its stronger pedicle fold and brachial sulcus and its lesser convexity. 
The species may be a composite one because the holotype is stratigraphically 
younger than the New York specimens. 
MULTICOSTELLA PLENA Cooper, new species 
Plate 62, B, figures 6-14 
Shell small for the genus, slightly wider than long, and with the greatest width 
at about the middle. Cardinal extremities acutely to obtusely angular, rarely 
auriculate. Both valves moderately convex, the brachial valve generally the 
deeper. Anterior commissure rectimarginate. Surface multicostellate, 10 to 12 
costellae occupying a distance of 5 mm. at the front. 
Pedicle valve unevenly convex in lateral profile, with the greatest convexity in 
the posterior half and the front half flattened or depressed. Fold nearly obsolete, 
best developed in the posterior half. Flanks flattened and sloping gently away 
