PENNAT.E 



Valve zygomorphous. Structure pinnate, not concentric. Valve divided either by a 

 true raphe or cleft or by a linear space or line imitating a raphe. 

 Divided into three Groups : 



1. Fragilarioidece. Valves without a raphe; usually with a pseudoraphe or median line. 



2. Naviculoidece. Either one or both valves with a true raphe. 



3. Surirelloidece. Valves in which the raphe is concealed near the margin on one or 

 both sides of each valve in a more or less elevated keel or wing. 



FRAGILARIOIDE^ 



(a) Tabellariece. Valve symmetrical with respect to both the longitudinal and trans- 

 verse axes; septate, not cuneate. 



(6) Meridionece. Valve symmetrical with respect to the longitudinal axis, asymmetri- 

 cal to the transverse axis, cuneate, finely striated. 



(c) Fragilariece. Valve of varied shape, not cuneate; costate or with transverse rows 

 of puncta. 



(a) TABELLARIE.E 



Frustule in zone view rectangular, in valve view linear or linear-elliptical, sometimes 

 constricted in the middle, symmetrical to both axes, not cuneate; with two or more septa 

 or annuli. 



Chromatophores numerous, granular. 



Rhabdonema. Frustules with numerous septate partitions having one or several 

 foramina. Transverse costse or rows of coarse puncta. 



Tabellaria. Frustules with two to six nearly straight septa. Transverse striae subtly 

 punctate. 



Grammatophora. Frustules with two sinuate perforate curved septa. Transverse 

 striae subtly punctate. 



Striatella. Frustules with alternate partitions, septate or partly so. 



Attheya. Frustules not septate but with numerous annuli. 



RHABDONEMA KUETZ. (1844) 

 (rhabdos, a rod, and nema, a thread) 



Frustules quadrangular, concatenate, composed of numerous septate partitions with 

 transverse costa? or rows of puncta. Valves elliptical, with a pseudoraphe and transverse 

 apparent costse and punctate lines; the partitions with one or several foramina. 



Chromatophores in rosettes of various kinds (Karsten) ; usually parallel to the septa. 



RHABDONEMA ARCUATUM (LYNG.) KUETZ. 



Valve hyaline at the ends, with transverse rows of puncta producing the appearance 

 of costse between the rows; pseudoraphe distinct; foramen single. 

 Diatoma arcuatum Lyngbye. 

 Common along the coast. 

 PI. 8, Figs. 1, 2, and 3; PI. 40, Fig. 10. 



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