64 THE DIATOMACE^E OF PHILADELPHIA AND VICINITY 



radiate, distant in the middle of the dorsal side where they are 7 in 10 n, coarsely punctate, 

 the puncta in longitudinal lines, 9 in 10 M on the ventral side, closer at the ends. L. 69 n. 



Baker's Run, Willistown, Pa. 



PL 18, Fig. 11. 



CYMBELLA GRACILIS (RAB.) CL. 



Valve semi-lanceolate, with acute ends; median line nearly straight, with terminal 

 fissures turned downwards, distant from the ends; axial area linear; ventral margin straight 

 or slightly gibbous in the middle. 



Hammonton Pond, N. J. 



PL 18, Fig. 20. 



CYMBELLA LACUSTRIS (AG.) CL. 



Valve elliptical-lanceolate, with obtuse ends, nearly symmetrical; median line straight) 

 terminal fissures distant from the ends; strise radiate in the middle, convergent at the ends, 

 coarsely lineate. 



Belmar, N. J. 



PL 18. Fig. 25. 



AMPHORA EHR. (1840) 

 (amphora, a jar) 



Valves asymmetrical along the longitudinal axis, as in Cymbella, but with the plane 

 passing through the dorsal and ventral sides of one valve at an angle with that of the other. 

 As Cleve states, Cymbella and Amphora are forms of Navicula "with both valves similar 

 and asymmetrical along the longitudinal axis," and the difference between Cymbella and 

 Amphora is in the "degree of asymmetry." If, following H. L. Smith's diagrams (Lens, Vol. 

 2, 1873, p. 66), we assume that the usual form of the valve in Navicula is elliptical or lan- 

 ceolate, and the zone view is rectangular, we have in Cymbella an arcuate median line and 

 a more or less reniform valve, while the zone view remains rectangular with the valves 

 parallel. Now, if the valves are asymmetrical along the longitudinal axis, and one side of 

 one valve is separated from the corresponding side of the opposite valve by a wider connec- 

 tive zone than is the case on the other side, the transverse section of the frustule will appear 

 cuneate, as in Amphora, and the connective zone will be wider on one side than the other. 

 When, therefore, we examine an entire frustule as it is usually seen, we shall find the two 

 raphes of the valves in focus at the same time on the ventral side, and, by changing the 

 focus, the convex sides of the same valves are seen, the dorsal view with, usually, a wider 

 connective zone. As an illustration, compare Figs. 5 and 6, on Plate 15, Fig. 6 being the 

 ventral, and Fig. 5 the dorsal view. 



As Amphorae are epiphytic or parasitic, they are considered, as Cleve remarks, like 

 Achnanthes and Cocconeis, as "degenerated forms." 



Chromatophores usually single, lying on the ventral connective zone. Mereschkowsky 

 describes nine forms. 



Cleve divides the genus into a number of groups as follows: 



Amphora proper. Connective zone not complex; valves with longitudinal lines on the 

 dorsal side; coarsely punctate or costate. 



Diplamphora. Zone complex; otherwise as in Amphora. 



Halamphora. Longitudinal lines absent; frustule elongate, with protracted ends. 



