\\ 



v 





FRAGILARIA. 



a. b. 



Fig. 79. Fragilaria 

 virescens. 



3 2 3 



GENUS 44. FRAGILARIA LYNGBYE, 

 1819 (Char. Emend). 

 Valves symmetrical without costa?. Frus- 

 tules rectangular, united in long filaments or 

 chains. In the section Staurosira the endo- 

 chrome is similar to that of the Synedra. In 

 the species contained in the section Fragilaria, 



a. Valve, b. Girdle view, it is granular. 



Pseudo- 



raphe 



narrow and 



scarcely 



visible 



[Fragilaria). 



Pseudo- 



raphe 



distinct 



(Staurosira). 



ANALYSIS OF SPECIES. 



Valve linear or linear-elliptic, with apices produced ; striae 



17 in 1 c.d.ni. Fresh water species . . F. virescens. 



Valve elliptic-oval, with apices acuminate-rostrate. Fresh 

 water . . . . . F. undata. 



Valve elliptic-elongated, scarcely silicious ; striae very 



delicate, 24 in 1 c.d.m. Marine . . . F. striatula. 



Valve linear-narrow, with apices inflated ; striae almost 



invisible, 31 or 32 in 1 c.d.m. Marine . . F. hyalina. 



Valve linear, very narrow, inflated at the median portion. 

 Fresh water .... 



Striae formed of distinct beads 



. F. Crotonensis. 

 F. capucina. 



Striae 

 not 

 margi- 

 nal. 



Striae very 

 robust, 

 i with beads 

 more or 



less 

 confluent 



or 



simulating 



costae. 



Valves 

 small, 

 broad- 

 ly oval 



or 

 cruci- 

 form . 



Valve small, either 

 cruciform, or inflated 

 or constricted at the 

 median portion, striae 



fine 



. F. construens. 



Striae marginal 



Valve narrowly lanceo- 

 late, with apices in- 

 flated, capitate. Fresh 

 water - . F. tenuicollis. 



Valve regularly oval . F. mutabilis. 



Valve cruciform, rather large, 

 with robust costae . . F. Harrisonii. 



. F. brevistrlata. 



I. Fragilaria. Pseudo-raphe very narrow and scarcely visible. 



F. virescens Ralfs. (Ann. and Mag., 1843, XII., p. no, pi. 2, f. 6; 

 H.V.H. Atl., pi. 44, f. 1* ; Type No. 309), plate n, fig. 442. 



Valve linear or linear elliptic, with apices attenuate and often rostrate- 

 obtuse. Pseudo-raphe scarcely visible. Striae fine, distinctly punctate, about 

 17 in 1 c.d.m. Frustules quadrangular, elongate, united in long filaments. 

 Length of valves very variable. Mean length, 2 to 6 c.d.m. 



Fresh water. Southern region of Belgium: Namur (P. Gaut.). Pleinevaux (Delogne). Ard. 

 Lieg. (De Wild.). England, Scotland, Ireland, and throughout Europe. 



