THE DIATOMACE^E OF PHILADELPHIA AND VICINITY 57 



COCCONEIS EHR. (1835) em. GRUN. (1868) 

 (coccos, a berry) 



Valves elliptical, dissimilar, the upper valve with a pseudoraphe and the lower with a 

 genuine raphe and nodules, usually with a rim or annulus. Frustules epiphytic. 



Cocconeis is generally considered as a degenerated form of Mastogloia, as indicated by 

 the "obsoletely loculiferous rim." The frustules are usually bent along the longitudinal 

 axis, probably because of the attachment to the curved stems of water-plants. 



The cell contents of only a few species are known. In C. pediculus, a single chromato- 

 phore occurs on the inside of the upper valve. In conjugation, two cells open and secrete 

 a gelatinous mass from which an auxospore is formed. 



Cleve separates the forms having a loculiferous rim (Cocconeis) from those without a 

 rim (Eucocconeis). As the rim is easily detachable, the distinction is often made with 

 difficulty. 



COCCONEIS SCUTELLUM EHR. 



Valves elliptical, the upper with a linear or lanceolate pseudoraphe and coarse puncta 

 in transverse and radiating lines; the lower valve with much finer puncta in radiating lines, 

 a lanceolate axial area and, sometimes, a loculiferous rim. 



Along the coast. Common, but extremely variable. 



PL 16, Fig. 21 (upper valve). Fig. 18, var. ? 



COCCONEIS SCUTELLUM VAR. ORNATA GRUN. 



Upper valve with linear axial area, and transverse and radiating punctate lines which 

 end at the border in a double row of finer puncta; lower valve with much finer puncta, a 

 lanceolate axial area and a loculiferous rim. 



Atlantic City. Common. 



PI. 16, Figs. 27 and 28. 



The forms along the coast vary infinitely both in size and appearance. The var. 

 ornata is very abundant along the entire coast. In any gathering, valves are found with 

 or without the rim which is frequently seen detached. The upper valve is sometimes with- 

 out the double row of puncta. Fig. 21 represents an upper valve more coarsely punctate 

 than usually occurs. Very many intermediate forms might be noticed. 



COCCONEIS PEDICULUS EHR. 



Valves rhombic-elliptical, very convex, somewhat asymmetrical; the upper valve with 

 a linear pseudoraphe, sometimes widened near the ends, and slightly radiating, finely punc- 

 tate striae; lower valve with narrow, axial area and finely punctate, radiating striae. 



Not uncommon in fresh water. Abundant in a ditch at Paoli, Pa. 



PI. 16, Figs. 23 and 24. 



COCCONEIS PLACENTULA EHR. 



Valve elliptical; upper valve with a linear or lanceolate axial area, and punctate striae 

 in transverse and radiating rows, the puncta at equal distances; the lower valve with a 

 lanceolate axial area, radiating rows of puncta, and a wide border of finely punctate, 

 radiating stria?, separated from the central part of the valve by a narrow hyaline zone. 



Common in salt, brackish and fresh water. 



PI. 16, Figs. 19 and 20. 



