MARYLAND GEOLOGICAL SURVEY 267 



This species belongs to the genus or subgemis Cliftonia established by 

 Foerste for the plicated forms of Triplecia, which was well described as 

 Oxoplecia by Miss Alice Wilson. Triplecia (Cliftonia) simulatrix is 

 related to Oxoplecia calhouni Wilson, from the base of the Collingwood 

 (Trenton) shale of Ottawa, Canada, but differs in its coarser plication, 

 this feature being most marked on the sides of the shell. 



Occurrence. MABTINSBURG SHALE (Sinuites bed). One mile south 

 of St. Thomas, Pennsylvania, and at Strasburg, Virginia. The species 

 occurs also in the Echinospherites, Nidulites, and Christiania beds of the 

 Chambersburg limestone in Pennsylvania, Maryland, and Virginia. 



Collections. Maryland Geological Survey, U. S. National Museum. 



Superfamily PENTAMERACEA 



Family SYNTROPHIIDAE 



Genus SYNTROPHIA Hall and Clarke 



SYNTROPHIA LATERALIS (Whitfield) 



Plate XXXIII, Figs. 4, 5 



Triplesia lateralis Whitfield, 1886, Bull. Amer. Mus. Nat. Hist., p. 303, 



pi. xxiv, figs. 9-11. 

 Syntrophia lateralis Hall and Clarke, 1892, Pal. New York, vol. viii, pt. 1, 



p. 270; ibid., vol. viii, pt. 2, p. 216, pi. Ixii, figs. 1-10. 

 Syntrophia lateralis Weller, 1903, Geol. Surv. New Jersey, Pal., vol. ill, 



p. 126, pi. iv, figs. 14, 15. 

 Syntrophia lateralis Walcott, 1912, Mon. U. S. Geol. Surv., vol. li, p. 802, 



text fig. 11, p. 299; pi. cii, figs. 6, 6a-g. 



Description. Shell averaging 7.5 mm. in length and 11 mm. wide, 

 subelliptical, with the hinge-line about two-thirds the greatest width and 

 the cardinal extremities rounded. Pedicle valve somewhat convex, promi- 

 nent on the umbo, but a little flattened near the cardinal angles; beak 

 slightly incurved and rather blunt, projecting beyond the cardinal mar- 

 gin; mesial sinus broad, shallow, and ill-defined, not extending to the 

 beak. Surface with fine, concentric lines of growth. 



Occurrence. BEEKMANTOWN LIMESTONE (Cryptozoon steeli zone). 

 At various localities around Williamsport and Hagerstown, Maryland. 



Collections. Maryland Geological Survey, U. S. National Museum. 



