58 THE DIATOMACE^ OF PHILADELPHIA AND VICINITY 



COCCONEIS PLACENTULA VAR. LINEATA (EHR.) V. H. 



As in the type, except that the upper valve has the puncta arranged in zig-zag, giving 

 the appearance of sinuous, longitudinal lines. 



Common along the coast. 



PL 16, Fig. 29. 



C. pediculus and C. placentula are the only species I have found in fresh water. Cleve 

 states that the former occurs also in brackish water. 



The following are among the species placed by Cleve in a new genus, Eucocconeis, 

 distinguished by the absence of a loculiferous rim. 



COCCONEIS DIRUPTA GREG. 



Valves elliptical, the lower with fine puncta in slightly radiating lines, a narrow axial 

 area and a central area dilated into a lanceolate, stauriform space; the terminal fissures 

 turned in opposite directions; the upper valve similar to the lower valve except in the ab- 

 sence of raphe and nodules. 



Along the coast. New Rochelle. 



PL 16, Fig. 22 (lower valve). 



COCCONEIS PELLUCIDA GRUN. 



Valves elliptical, the upper with broad axial area on each side of which are fine, lon- 

 gitudinal rows of short striae ; the lower valve with more numerous longitudinal rows, a mar- 

 ginal line and indistinct raphe; the terminal fissures small and turned in opposite directions. 



New Rochelle. 



PL 16, Figs. 25 and 26. 



In the var. minor Grun. the median line of the lower valve is sometimes slightly 

 sigmoid. 



ACHNANTHES BORY (1822) 

 (achne, froth or down, and anthos, a flower) 



Frustules stipitate, solitary or in short fasciae, flexed. Valves elliptical or lanceolate, 

 naviculoid, dissimilar, the lower with a raphe and median and terminal nodules, and the 

 upper with a pseudoraphe or median space. 



The genus has no apparent affinity with any other. 



ACHNANTHES LONGIPES AG. 



Valves linear-elliptical, obtuse at the apex, sometimes slightly constricted in the middle. 

 Connective zone with transverse, subtly punctate striae, interrupted by longitudinal lines. 

 Central nodule of lower valve dilated into a stauros reaching the margin. Valves costate, 

 the costae alternating with double rows of fine puncta. 



Along the coast, in estuaries. 



PL 16, Figs. 1 and 2. 



A. longipes is the only species in our locality considered by Cleve as belonging to the 

 genus; the other forms, distinguished by the absence of costae, are included in the genus 

 Achnanthidium of Kuetzing. 



In A. longipes, the chromatophores consist of scattered, rounded granules, while in 

 Achnanthidium the chromatophore is a single plate along the upper valve, or a double one 



