54 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 134 
STENOSCISMA cf. S. PLICATUM (Kutorga) 
Plate 10F, figures 32-35 
Pentamerus plicatus Kutorca, Verhandl. Russ-Kais. Min. Ges., St. Petersburg, 
p. 89, pl. 9, fig. 3, 1844. 
Camarophoria plicata (Kutorga) TscHERNyscHEW, Mém. Com. Géol., St. 
Petersburg, vol. 16, No. 2, pp. 92, 502, pl. 21, fig. 1, pl. 50, figs. 17, 18, 1902. 
Several specimens of a large but poorly preserved Stenoscisma are 
compared to Kutorga’s species. An uncrushed pedicle valve is 27 mm. 
long by 30 mm. wide at the widest part which is anterior to the mid- 
dle. The sulcus originates near the middle and is occupied by 5 cos- 
tae and the flanks by 6 costae. 
A crushed complete specimen shows a long tongue on the pedicle 
valve and a low fold occupied by 6 costae. Although the two speci- 
mens do not attain the full size of Kutorga’s species, the characters 
indicated are in accord with the Russian species. 
Types.—Figured specimens, U.S.N.M. 125385a,b. 
Localities —S87, S103, S106; U.O. 2201-4, 2202-1, 2202-2, 2202-6. 
Superfamily RayNcHoporAcea Moore, 1952 
Family RHYNCHOPORIDAE Muir-Wood, 1955 
RHYNCHOPORA MAGNA Cooper, new species 
Plate oA, figures I-10; plate 10D, figures 18-31 
Sheil large for the genus, pentagonal in outline, triangular in lateral 
profile. Beak obtuse, greatest width slightly anterior to the middle. 
Greatest thickness at the anterior. Anterior margin slightly convex. 
Shell provided with 24 to 26 costae, with 8 on the fold, 7 in the 
sulcus, and 9 on the flanks. 
Pedicle valve gently convex in lateral profile, with the anterolateral 
flanks reflected. Maximum convexity slightly posterior to the middle. 
Umbo and median region slightly inflated; sulcus originating at the 
middle, shallow and broad, slightly swollen in the middle and occupy- 
ing slightly more than half the width. Flanks bounding sulcus slightly 
concave posteriorly but anterolaterally folded into a low plica. Tongue 
long and truncated in front. Interior with long, stout dental plates. 
Brachial valve gently convex in lateral view, narrowly convex in 
anterior profile; umbonal and median regions slightly swollen. Fold 
low and broad, originating at about the middle, protruding slightly 
anteriorly ; flanks rounded and extended, with steep slopes and with 
sharp geniculation to unite with the reflected anterolateral extremities 
of the pedicle valve. 
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