84 THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 



NEIDIUM IRIDIS (EHR.) CL. 



Valve linear or lanceolate-elliptical, with sub-cuneate or rounded ends; striae oblique, 

 about 18 in 10 y.; central area orbicular. 



Navicula iridis Ehr. 



Navicula firma Kuetz. 



Willistown, Pa.; Middletown, Delaware Co., Pa. (Palmer). 



PL 21, Fig. 17. 



The form here figured is probably the variety ampliata (Ehr.) CL with less acute 

 apices and more elliptical outline. The species occurs in many variations, the larger being 

 found northward, especially in the peat deposits of New England. 



NEIDIUM HITCHCOCKII (EHR.) CL. 



Valve linear, with triundulate margin and cuneate ends; strise transverse, oblique. 



Navicula hitchcockii Ehr. 



Pavonia, N. J. (artesian well) ; Kirkwood Pond, N. J. 



PL 21, Fig. 15. 



DIPLONEIS EHR. (1840) 



(diplos, double) 



Valve elliptical or panduriform; median line enclosed in strongly siliceous horns cor- 

 responding to the lyre-shaped areas of Navicula lyra but never punctate; central nodule, 

 quadrate ; valve costate, or striate, or both ; between the horns and the outer part are thinner 

 spaces or sulci, and, in some species, outside of the sulci are narrow spaces known as lunulse. 



Chromatophores, two, upon the girdle or the valves. Pyrenoids have been found in 

 one species only, D. interrupta. 



DIPLONEIS ELLIPTICA (KTJETZ.) CL. 



Valve elliptical; central nodule large; sulci narrow, curved, close to the horns; strise 

 punctate, in rows radiating more and more toward the ends. Variable in size and in the 

 coarseness of puncta which are from 10 to 13 in 10 n (Cleve). 



Cleve describes D. ovalis Hilse as having the central nodule rounded, but otherwise 

 about the same as D. elliptica, and as equivalent to Navicula ovalis A. Schmidt (Atlas, 

 PL 7, Figs. 33 to 36). 



Very common in fresh water and occasional in brackish. 



PL 20, Fig. 14. 



DIPLONEIS SMITHII (BREB.) CL. 



Valve elliptical; central nodule not broad; furrows evenly curved on the outer edge, 

 crossed by costse and double oblique rows of alveoli. Variable in size and in the curvature 

 of the furrows. 



Cleve forms a new species, D. major, of the large form figured by Schmidt (Atlas, PL 

 7, Figs. 18, 19, 21 and 22), stating that the structure is much coarser and the form is larger 

 with broad furrows. In the specimen here figured the size is median and the furrows are 

 as in D. major. 



Marine and brackish. Common. 



PL 20, Fig. 17. 



