DIATOMACEvE. 



[ 255 ] 



DIATOM ACE <E. 



[Sphenella. Fr. free, solitary, wedge- 

 shaped, involute; freshwater (PI. 19. 

 fig. 19). 



Sphenosira. Fr. united into a straight 

 filament ; \. wedge-shaped, at one end 

 rounded, suddenly contracted and pro- 

 duced : freshwater (PI. 17. fig. 26).] 

 Coh. 11. NAVICULEJE. Fr. free, straight j 

 v. equilateral, or sometimes sigmoid. 



Navicula. Fr. single, free, straight; v. 

 oblong, lanceolate or elliptical, with a 

 median line, a central and two termi- 

 nal nodules, and transverse or slightly 

 radiant lines resolvable into dots ; 

 freshwater, marine, and fossil (PI. 15. 

 figs. 6-9). 



(Stigmaphora.} 



Pleurosiama. Fr. those of Navicula, but 

 valves sigmoid ; freshwater and marine 

 (PI. 15. figs. 10-38). 



(Toxonidea.) 



Pinnularia. Fr. those of Navicula, but 

 transverse lines continuous and not re- 

 solvable into dots ; freshwater and ma- 

 rine (PL 15. figs. 1-5). 



Stauroneis. Fr. those of Navicula, but 

 the median nodule replaced by a stau- 

 ros; freshwater and marine (PI. 15. 

 figs. 43-45). 



Staurosigma. Fr. those of Stauroneis, 

 with a sigmoid longitudinal line. 



Diadesmis. Fr. those of Navicula, united 

 into a straight filament; freshwater 

 (PI. 16. fig. 27). 



Amphiprora. Fr. free, solitary or in 

 pairs, constricted in the middle ; v. 

 with a median keel, and a median and 

 terminal nodules, often twisted : marine 

 (PL 16. fig. 8). 



(Donkinia.) 



Amphora. Fr. plano-convex, elliptical, 

 oval or oblong, solitary, free or adnate, 

 with a marginal line and a nodule or 

 stauros on the flat side; freshwater 

 and marine (PL 16. figs. 10, 11). 



Perizonium. Frustules navicular, free, 

 with thickened zones (PL 51. fig. 42.) 



Tribe II. Vitiate. Fr. with vittae. 



t Valves without a median nodule. 

 Coh. 12. LICMOPHOBE^J. Fr. cuneate; 

 vittae arched. 



Licmophora. Fr. cuneate, rounded at the 

 broad end, radiating from a branched 

 stalk ; vittae curved (formed by inflec- 

 tion of the upper margins of the valves) ; 

 marine (PL 17. fig. 3), 



Podosphenia. Fr. those of Licmophora 

 but single or in pairs, sessile upon a 

 thick but little-branched pedicel ; ma- 

 rine (PL 17. fig. 17). 

 Rhipidophora. Fr. those of Licmophora, 

 single or in pairs, upon a branched 

 stipes ; marine (PL 17. fig. 19). 



Climacosphenia. Fr. cuneate, rounded at 

 the broad end, divided into loculi by 

 transverse septa or vittse ; marine (PL 

 25. fig. 9). 



Coh. 13. STRIATELLEJE. Fr. tabular or fila- 

 mentous; vittse straight (not arched). 



Striatella. Fr. compound, stalked at one 

 angle ; vittae longitudinal and conti- 

 nuous ; v. elliptic-lanceolate, not stri- 

 ated (ord. ilium.) ; marine (PL 17. fig. 

 20). 



Rhabdonema. Fr. as in Striatella, but 

 vittse interrupted, and v. with trans- 

 verse granular striae ; marine (PL 17. 

 fig. 18). 



Tetracyclus. Fr. compound, filaments 

 compressed ; vittae alternate, interrup- 

 ted; v. inflated at the middle; costae 

 transverse, continuous ; freshwater (PL 

 17. fig. 28). 



Tabellaria. Fr. united into a filament, 

 subsequently breaking up into a zigzag 

 chain ; vittse interrupted, alternate ; v. 

 inflated at the middle and ends ; fresh- 

 water (PL 17. fig. 27). 

 \_Pleurodesmium. Fr. tabular, united into 

 a filament, and with a transverse me- 

 dian hyaline band ; marine. 



Hyalosira. Fr. tabular, fixed by a stalk 

 at one angle; vittae alternate, inter- 

 rupted, bifurcate at the end; marine 

 (PL 17. % 1). 



Anaulus. Fr. rectangular, single, com- 

 pressed, with lateral inflections, giving 

 the valves a ladder-like appearance ; 

 marine (PL 18. fig. 7). 



Biblarium. Fr. as in Tetracyclus, but 

 single ; fossil (PL 50. fig. 39 ; PL 18. 

 figs. 35-48). 



Terpsinoe. Fr. tabular, obsoletely stalked, 

 subsequently connected by isthmi ; 

 vittse transverse, short, interrupted 

 and capitate; freshwater and marine 

 (PL 25. fig. 10; PI. 19. fig. 33). 



Stylobiblium. Fr. compound; v. circu- 

 lar, sculptured with continuous striae ; 

 fossil (PL 18. fig. 50).] 



ft V. with a median apparent (pseudo-) 

 nodide. 



Grammatophora. Fr. at first adnate? 



