SURIRELLA. 



3 6 9 



ANALYSIS OF SPECIES. 



a! 

 > 



Valves 



showing 



robust 



costse 



throughout 



their 



length and 



reaching 



to the 



median 



line. 



f Valve small, linear or ellip- 



The two apices equally 

 conical. 



tic 



Valve 

 late 



very large, lanceo- 



I 



Valve of medium size, lan- 

 ceolate, constricted at 

 middle 



Valve 

 oval , 

 one 

 apex 

 acute, 



the 

 other 

 obtuse 



I Striae not reaching to the pseudo- 

 raphe ;si?e very considerable 



Striae 



reach- 

 ing 

 to the 

 pseudo 

 raphe. 



Costa leaving no 



space free except 



a very narrow 



pseudo-raphe. 



Size very small, 

 striae robust 



Size very large, 

 strife fine . 



S. linearis. 

 S. biseriata. 



S. Smithii. 



S. elegans. 

 subsala 

 Gemma. 



s 



I 



t 



Costa: 

 leaving 

 near the 

 pseudo- 

 raphe a 

 rather 

 broad 

 striated 

 space. 



I Valve longly oval ; alas 

 very robust, more or 

 less approximate to 

 the connecting zone. S. robusta. 



I V 



I 



rive broadly oval ; 

 alas conspicuous, 

 quite marginal 



S. striatula. 



I 



Costa- 

 marginal 



or 



becoming 



more 



feeble 



near the 



centre of 



the valve. 



Costa- very robust on the margin of the valves, becoming 

 more feeble near the median portion. Marine species, 

 very robust . . . . . S. fastuosa. 



As the preceding, but costre leaving a lanceolate blank 



space. Fresh and brackish water . . S. turgida 



Costa: marginal or becoming very delicate near the 

 central portion of the valve. Fresh or brackish water 

 species. Rather delicate . . . S. ovalis. 



[ Valves twisted round the pseudo-raphe. Frustule in form of figure 8 



S spiralis. 



/. Valves plain. 



A. Valves showing robust costae throughout their length, and reaching 



to the median line. 



,7. THE TWO Al'ICES OF THE VALVE EQUALLY CONICAL. 



S. biseriata Breb. (Aig. Falaise, pi. 7 ; h.v.h., pi. 72, f. j to 



3*; Type Nos. 420, 421), plate 12, fig. 575. 



Valve broadly lanceolate, with apices sometimes somewhat sub-rostrate, 

 sub-obtuse, with costae robust, the median straight, the terminal radiant. 

 Pseudo-raphe with hyaline area of more or less breadth, and more or less 

 lanceolate. Striae very delicate. Girdle face linear, oblong, with rounded 

 angles, showing the keel alate, robust. Length, 10 to 17 c.d.m. 



Fresh water. Rather common throughout Europe. 



A A 



