326 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Arline formation in Virginia: Quarry on north side of Marion, Marion 
(T.V.A. 218-SE) Quadrangle. 
Discussion——This species is closest to C. subplana but differs in having a 
more concave brachial valve, less numerous, narrower, and more elevated cos- 
tellae and more swollen umbonal region on the pedicle valve. 
CYRTONOTELLA ? sp. 1 
Plate 32, F, figures 16-21 
Under this heading is placed a lot of six specimens that have suffered some 
distortion with the result that uncertainty exists as to their proper classification. 
The shells are finely costellate with about 3 costellae to the millimeter. They are 
concavo-convex to nearly planoconvex, and the brachial interiors are most like 
Cyrtonotella. The species are suggestive of the fine-lined Cyrtonotellas that oc- 
cur in the Hogskin member of the Lincolnshire formation, the Red Knobs forma- 
tion (not described), and possibly the Benbolt formation. 
Figured specimens.—109867a-d. 
Horizon and locality—Botetourt formation in Virginia: On Hays Creek, 2 
miles northeast of Brownsburg, Lexington (15’) Quadrangle. 
TAPHRORTHIS Cooper, new genus 
(Greek taphros, ditch) 
Shell subquadrate to subrectangular in outline; sides rounded; anterior mar- 
gin gently rounded to truncate; hinge straight, generally narrower than the 
greatest shell width which is usually at or near the middle ; biconvex, the pedicle 
valve having the greater convexity; surface costellate, costellae appearing in 5 
generations, 1 at the beak, 1 on the anterior slope of the umbo, and 3 anterior 
to the umbo; spaces between costellae and surface of costellae occupied by coarse 
concentric fila. 
Pedicle valve with delthyrium modified by more or less clearly defined lateral 
plates ; teeth small, triangular, with shallow fossettes ; dental plates short, reced- 
ing and divergent; umbonal cavities mostly filled by callus; delthyrial cavity 
wide and deep; muscle field orthoid extended anterior to the ends of the dental 
plates ; muscle field crudely heart-shaped ; diductor scars large, linear ; adductor 
field small, divided by a median ridge extending as far as the middle; vascula 
media not strongly impressed. 
Brachial valve with fairly deep notothyrial cavity ; notothyrial platform thick, 
continuous with the median ridge which is low, narrow, and extends to about 
the middle of the valve; anterior of notothyrial platform somewhat excavated ; 
brachiophores short, supported by callus on the inner edge of the notothyrial 
platform; cardinal process poorly developed forming a low, inconspicuous ridge. 
Adductor field large. 
Genotype.—Taphrorthis emarginata Cooper, new species. 
Discussion——Of described genera, Taphrorthis most resembles Glossorthis 
Opik from the Middle Ordovician of Estonia. The two genera differ in many 
