THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 65 



Oxyamphora. Zone complex; longitudinal lines absent; frustule elliptical; valve 

 lunate, with or without a central stauros; striae punctate. 



Amblyamphora. Zone complex; frustule rectangular; valve lunate; striae punctate; 

 axial and central areas indistinct. 



Psammamphora. Zone not complex; frustule rectangular; central nodule frequently 

 dilated to a stauros; no axial or central area. 



Cymbamphora. Valve semi-lanceolate; median line straight, approximate to the ven- 

 tral margin. 



AMPHORA 



AMPHORA ROBXJSTA GREG. 



Frustule elliptical, truncate; valve lunate, with straight ventral margin; median line 

 biarcuate; ventral side with coarse, radiate striae, 6 in 10 n, on both sides of the median line. 

 Along the coast. 

 PL 15, Fig. 1. 



AMPHORA PROTEUS GREG. 



Frustule elliptical, truncate; valve lunate, with straight ventral margin; median line 

 biarcuate; no central area. Striae on the dorsal side not interrupted, 9 in 10 ju. Ventral 

 side striate toward the ends. 



Differs from A. robusta chiefly in size and coarseness of puncta. Extremely variable 

 in size. 



Common along the coast. 



PL 15, Figs. 5, 6, and 19. 



AMPHORA OVALIS (fiREB.) KUETZ. 



Frustule elliptical, truncate; valve lunate; median line biarcuate; striae on dorsal 

 side 10-16 in 10 /*. 



Var. libyca (Ehr.) Cl. Central area distinct on the dorsal side. 



Var. pediculus (Kuetz.) Cl. Central area and nodule quite distinct. Striae finer than 

 in var. libya. 



Common in ponds. Quite variable. 



PL 15, Fig. 7. 



AMPHORA GIGANTEA VAR. FUSCA A. S. 



Frustule elliptical; valve lunate, with straight ventral margin. Axial area absent on 

 the dorsal side; dorsal striae, 10 in 10 ju, punctate. Ventral part hyaline except at the ends, 

 which are obliquely striated, with short, punctate lines. L. 70-120 n. 



Absecon, N. J. 



PL 38, Fig. 1. 



DlPLAMPHORA 

 AMPHORA CRASSA GREG. 



Valve linear-elliptical, with obtuse, incurved ends. Median line biarcuate. Axial and 

 central areas indistinct on the dorsal side; striae coarsely punctate, interrupted by a longi- 

 tudinal line on the dorsal side. 



Along the coast. 



PL 15, Fig. 3. 



