924 



SYSTEMATIC HISTOET OF THE rNTTJSOEIA. 



2 * Frustules naviculold, envelojped in gelatine or enclosed in a definite 

 tubular or gelatinous frond. 



Subfamily SCHIZONEME^ or LACERNAT^. 



This group is remarkable for the great external resemblance some of its 

 species have to acknowledged Algae, widely as they differ in internal structure. 



Genus ERUSTULIA (Ag.). — Erustules bacillar or navicular, immersed in 

 an amorphous gelatinous substance. For the present we retain this genus 

 in the Schizonemese, but believe that, in most if not all the species, the frus- 

 tules are more like a Synedra than a Navicula, and want the central nodule 

 of the latter. 



t StriaB evident. 



Frustulia salina (E.). — Very narrow 

 linear, transversely striated ; in front view 

 with rounded ends, in lateral view sud- 

 denly acute. E Inf. p. 232. Saline 

 springs, Germany. 



2 1 Striae wanting, or very indistinct. 



F. Kiitzingiaiia (Rab.). — Smooth, lan- 

 ceolate, with truncate apices. Rab D, 

 p. 35, pi. 8. f. 3. = Synedra mucicola, KB. 

 p. 68, pi. 14. f. 5. On stones in a rivulet 

 near Nordhausen. 



F. minuta (Rab.). — Minute, linear, 

 smooth, in front view with truncate 

 apices ; valves with acutely cuneate ends. 

 Rab D. p. 35. t. 8. f. 4. = Synedra Frus- 

 tulum, KB. pi. 30. f 77. Fresh water. 

 Germany and Italy. It forms an olive- 

 brown gelatinous mass on stones, and 

 becomes green in drying. 



F. torfacea (Braun). — Rhomboid-lan- 

 ceolate, with obtuse apices, a stout me- 

 dian rib, and small central nodule. RabD. 

 p. 50, t. 7. £ 2. Germany. It forms dirty- 

 yellow, rather firm, smooth or rugged 

 gelatinous masses about plants ui bogs. 

 An authentic specimen from Professor 



Braun appears to us identical with Na- 

 victda rhotnboides. 



F. Saxonica (Rab.). — Slenderer than 

 F. torfacea, ynih. valves more acute ; 

 front view linear, with broadly rounded 

 ends. Rab D. p. 50, t. 7. f 1. Saxony. 

 Forms dirty-olive-brown tremulous j elly- 

 like masses in little cavities of damp 

 rocks. 



F. Hcsckeriana (Rah.). — Valves spin- 

 dle-shaped, with acute, pointed endsj 

 front view narrow-lanceolate, with ob- 

 tuse apices. Rab D. p. 50, pi. 10. f 14. 

 Germany. Forms dirty gelatinous masses 

 on moss in streams. 



F. acicidaris (E.). — Bacilla slender, 

 smooth, with acute apices ; valves more 

 acute, like a fine needle. ERBA. 1853, 

 p. 527. Marine. Kingston Bay. Frus- 

 tules like those of Fragilaria Rhahdo- 

 soma, but free and heaped together 

 without order. 



F. hacillaris (E.). — Bacilla linear, pin- 

 nulate, with truncate apices in the front, 

 and rounded in the lateral view. EB. 

 1853. Marine. Kingston Bay. This 

 species, like F. acicidaris, seems included 

 in gelatine dilated like an idva, which, 

 when dry, appears membranaceous. In 

 the same membrane both species are in- 

 cluded, with many other Diatomacese. 



Genus MASTOGLOIA (Thwaites). — Frustules oblong, naviculoid, annulate, 

 in a gelatinous mammillate cushion or frond ; annuH loculated ; loculi open- 

 ing by foramina along the line of suture. ^' The frustules of Mastogloia 

 are notably distinct from those of the other genera of this tribe, having the 

 annulate structure of Rhabdonema with the canaliculi of Surirella." '' The 

 canaliculi are, however, formed differently from those of Surirella, not being 

 connected with the valve, but with the annulus, which projects as a septum 

 into the body of the frustule. The fmstule itself is ordinarily excentric to the 

 mucus developed around it, and sits as it were on the summit of a little 

 nipple-like cushion of gelatine " (Smith). 



Mastogloia Danseii (Thwaites). — 

 Valves elliptic-oblong, with 8 to 20 lo- 

 culi ; strij© 42 in -001". SB. ii. p. 64, 



pi. 62. £ 388. = Dickieia Banseii, ANH. 



1848. Brackish water. Britain. (xv.30.) 



M. lanceolata (Thw.). — Valves oblong- 



