432 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
line, large; adjustor impressions moderately developed; diductor scars large; 
dental plates short. 
Brachial valve strongly convex in lateral profile with the maximum convexity 
in the median region; anterior profile strongly convex and with steep slopes to 
the margins; umbonal region flattened, sulcate, sulcus short, shallow, narrow, 
extending to the middle ; median region, anterior, and flanks all swollen and with 
steep lateral and anterior slopes. Notothyrial platform thickened ; cardinal proc- 
ess slender; median ridge short. 
Measurements in mm.—Holotype, length 20.2, brachial length 21.6, width 24.7, 
hinge width 22.1, thickness 9.0. 
Types.—Holotype: 1081992 ; figured paratypes: 108199b-d. 
Horizon and locality—Plattin group (Macy formation) or Barnhart forma- 
tion in Missouri: On old road 1 mile northwest of Chicago Summer School 
Camp, NW4SW3 sec. 32, T. 37 N., R. 9 E.; on Fredericktown road 5 miles 
southwest of Ste. Genevieve, Weingarten (15’) Quadrangle ; Rockwood’s Reser- 
vation, 20 miles west of St. Louis on Manchester Road, 1 mile west of Grover, 
St. Louis County. 
Discussion.—This species is similar to C. deflecta (Conrad) in outline and 
ornamentation but differs in having a much less concave pedicle valve, a less 
strongly folded brachial valve, and much more strongly deflected cardinal ex- 
tremities. The Plattin form is, furthermore, a much more robust shell with 
greater depth and more strongly convex brachial valve. 
CHAULISTOMELLA Cooper, new genus 
Greek chauli, gaping; stoma, mouth) 
This name is proposed for shells morphologically intermediate between Multi- 
costella and Campylorthis. It is possible that the latter genus is more closely 
related to Valcourea, but some of the species of Chaulistomella closely resemble 
Valcourea and Campylorthis. Externally Chaulistomella is unlike Multicostella 
in having the anterior half of the pedicle valve deeply depressed or concave. In 
young forms or in a few species the resemblance to Multicostella is very strong 
and the genera are difficult to separate. Inside the pedicle valve the musculature 
is exactly like that of Multicostella, Campylorthis, and the rest of the Dinorthidae. 
The brachial valve of Chaulistomella is always strongly convex, but the cardi- 
nal process is not provided with a high median crest such as that of Valcourea. 
In this respect it is like Campylorthis but differs from that genus in not having 
a strong pseudodeltidium. The distinction between Multicostella and Chauli- 
stomella is thus based on the concave pedicle valve; the distinction between 
Chaulistomella and Campylorthis is based on the absence of a pseudodeltidium 
in the former genus. Not only is the pseudodeltidium absent from Chaulistomella, 
but no trace of it has been seen in any young specimens examined. 
Genotype.—Chaulistomella inequistriata Cooper, new species. 
