270 SYSTEMATIC PALEONTOLOGY 



of the shell. Pedicle valve depressed-convex, with an abrupt, broad, but 

 not deep sinus, which originates about one-third of the distance from the 

 beak to the anterior margin and is produced as a lingual extension in 

 front at nearly a right angle to the plane of the valve; it is marked by 

 from three to five radiating plications. The beak is small, closely in- 

 curved; delthyrium small and triangular. Brachial valve strongly con- 

 vex or gibbous, with a broad mesial fold commencing one-third of the 

 distance from the beak to the anterior margin, which is marked by from 

 four to six radiating plications. 



" The dimensions of a perfect individual are : Length, 13 mm. ; width, 

 16.5 mm.; thickness, 12.5 mm." Weller, 1903. 



Occurrence. CHAMBERSBURG LIMESTONE (Christiania bed). South- 

 ern Pennsylvania. Trenton limestone of New York, New Jersey, etc. 



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



order TELOTREMATA 



Superfamily RHYNCHONELLACEA 



Family RHYNCHONELLIDAE 



Genus CAMAROTOEGHIA Hall and Clarke 



CAMAROTOECHIA PLENA (Hall) 



Plate XLI, Figs. 14-16 



Atrypa plena Hall, 1847, Pal. New York, vol. i, p. 21, pi. iv, figs. 7. 

 Gamarotoechia plena Raymond, 1911, Ann. Carnegie Mus., vol. vii, p. 221, 

 pi. xxxiii, figs. 7-18. 



Description. " The adult shells are subtriangular to subcircular in 

 outline, with a wide, shallow ventral sinus and a somewhat elevated dorsal 

 fold. Surface marked by from 17 to 24 strong plications, four to seven 

 of which are in the sinus and five to eight on the fold. The plications 

 are crossed by zigzag lines of growth, which are sometimes stronger and 

 sometimes weaker on partially exfoliated specimens than of specimens 

 with perfect shells. The dorsal beak is strongly incurved, and the umbo 

 bears a slight median depression. The beak of the pedicle valve is only 



