792 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
the median one always present but others on the flanks usually visible. Sower- 
byella plicatifera is most like S. socialis and S. variabilis. It differs from the 
first in not being so robust, in being deeper, particularly along the posterior 
margin of the brachial valve, in being more finely costellate, and in having more 
prominent plicae. Sowerbyella plicatifera differs from S. variabilis in its stronger 
costellae, the prominent folding of the pedicle valve, and the less deep brachial 
valve. 
SOWERBYELLA PUNCTOSTRIATA (Mather) 
Plate 205, C, figures 9-25; plate 206, D, figures 14, 15 
Plectambonites punctostriatus MATHER, Ottawa Nat., vol. 31, p. 38, pl. 1, figs. 15-17, 1917. 
This species is widely identified in the lower part of the Trenton, particularly 
in New York and Ontario. The species is characterized by its large size and 
beaded ornamentation which gives the appearance of a pitted or punctate sur- 
face. It is most like S. curdsvillensis Foerste which is widely distributed in the 
Southern Appalachians and parts of the upper Mississippi Valley. Sowerbyella 
punctostriata is distinguished from S. curdsvillensis as follows: 1, lesser con- 
vexity and generally thinner valves; 2, less deeply concave brachial valve; 
3, greater development of the oblique wrinkles along the posterior margins; 
4, fairly late development of thickened subperipheral ridge in old adults; 5, lesser 
thickening of all internal structures; 6, greater tendency to auriculate cardinal 
extremities. 
Specimens in the National Museum indicate that this species is variable. Per- 
haps when its stratigraphic range has been more accurately worked out, some 
splits may be made from it. As indicated by topotypes the species is fairly thin 
shelled, only moderately convex, and the interior is scarcely thickened to a nota- 
ble degree. The amount of thickening of the internal structures and the develop- 
ment of a subperipheral rim were given by Mather as points of distinction be- 
tween S. punctostriata and S. curdsvillensis. Specimens referrable to the former 
species have been seen which have a prominent subperipheral rim and pro- 
nounced internal features. On the other hand, specimens referrable to the Ken- 
tucky species occur which do not have the strongly emphasized interiors. The 
degree of development of these features may be a matter of environment, the 
quiet-water limestone specimens having the delicate shell while the dwellers of 
sandy bottoms of the basal Martinsburg in the Southern Appalachians with its 
more turbulent water having the stronger shells. It is further possible that large 
suites of specimens will indicate that S. punctostriata and S. curdsvillensis are 
actually one species. 
Types.—Figured hypotypes: 117513a,b, 117514a,b, 117515a,b; figured topo- 
type: 117516. 
Horizon and locality—Rockland formation in New York and Ontario: Wolfe 
Island, Lake Ontario. 
Decorah formation (Guttenberg member) in Wisconsin, Iowa, Minnesota, 
and Missouri. 
Barnhart formation in Missouri: Koch Valley School, on U. S. Highway 61, 
NE. corner SW4SW3 sec. 6, T. 41 N., R. 6 E., 2 miles south of Barnhart, 
