OF THE FRAGILARIE^. 



779 



Inf. t. 15. f. 6 ; Diatoma cimeatum, Rab 

 D. t. 2. f. 4. Germany, (ix. 170.) Pro- 

 bably a state of D. vulgare. 



D. tenue (Ag.). — Valves lanceolate, 

 with from 9 to 12 distinct striae in 

 1-1200". Ag CD. p. 52 ; KB. p. 48, t. 9. 

 f. 10. = BaciUaria pectmalis^ E Inf. p. 198, 

 t. 15. f. 4. Europe and Asia. A protean 

 species ; the fi-ustules are sometimes qua- 

 drate, sometimes linear, and sometimes 

 cuneate. 



D. mesoleptum(K.). — Frustules slightly 

 attenuated at the middle ; valves lanceo- 

 late, with from 10 to 12 striae in 1-1200". 

 KB. p. 48, 1. 17. f. 16. Europe. 1-650". 

 We fear it is scarcely distinct from D. 

 tenue. 



D. Ehrenherciii (K.). — Front view at- 

 tenuated at the middle; valves linear 

 lanceolate, contracted beneath the sub- 

 capitate apices; costas 11 in 1-1200". 



KB. p. 48, 1. 17. f. 17 ; SA. 1857, xix. p. 10, 

 pi. 1. f. 13. = BaciUaria elongata, E Inf. 

 p. 198, t._15. f. 5. Europe, (ix. 169.) 

 The inflation in the centre of the valve 

 separates this species from D. grande, 

 which is moreover a larger form with 

 coarser striae, S, (iv. 15.) 



J}, grande (S.). — Valve linear, con- 

 stricted beneath the capitate apices ; 

 costfe 24 in -001". SBD. ii. p. 39, pi. 40. 

 f. 310. = Baci/laria australis, EM. pi. 35. 

 A 2. f. 3. Britain, Africa, and South 

 America. 



1). elongatum (Ag.). — Valves linear, 

 with inflated, capitate apices ; costae 7 in 

 1-1200". KB. p. 18, t. 17. f. 18 ; SBD. 

 ii. p. 40, pi. 40. f. 311. = Diatoma gracil- 

 limum, Nag., KSA. p. 889. Em-ope. 

 Front view slender, attenuated at the 

 middle, (iv. 14; ix. 119.) 



Genus ASTEBIONELLA (Hass.). — '' Friistiiles linear, inflated towards 

 one or both extremities ; adhering by their adjacent angles into a star-like 

 filament" (SBD. ii. p. 81). The frustules in this genus exactly resemble 

 those of the capitate species of Diatoma, but are few in number ; and being 

 connected by the adjacent angles, the free extremities diverge in a stellate 

 manner. We first observed a single specimen amongst some freshwater Algae 

 gathered near Dublin by Mr. D. Moore, and afterwards obtained it plentifully 

 for two successive years in a pool near DolgeUy, when we considered it a 

 species of Diatoma nearly allied to D. tenue. Subsequently we received a 

 larger form from Professor Dickie, gathered near Aberdeen. The Scottish 

 form had the free end truncated, and is probably the one described by 

 Professor Smith as A. Balfsii. 



AsTEBiONELLA fomiosa (Hass.). — 

 Front view somewhat more enlarged at 

 the base than at the summit. -0024" to 

 •0031". SBD. ii. p. 81. Fresh water. 

 Britain, (iv. 17.) 



A. Bleakeleyii (S.). — Frustules linear, 

 enlarged at the base. -0022". SBD. ii. 

 p. 82. Marine. England. 



{ A. Balfsii (S.). — Frustules in front 



view exactly linear ; valve attenuated at 



one end, constricted towards the other, 



: which is rounded and capitate; stria9 



I obscure. SBD. ii. p. 81. = Diatoina stel- 



lare, BO. p. 39. Fresh water, 

 and America, (iv. 18.) 



Europe 



Genus NITZSCHIA (Hass., Smith). — '' Frustules free, elongated, com- 

 pressed ; valves linear, keeled, with one or more longitudinal lines of puncta ; 

 keel frequently eccentric. . . . This genus embraces a large number of species, 

 diftering in form and size, but aU agreeing in a few general characters. The 

 most important of these is the keeled form of the valves and the remarkable 

 inequality, in many of the species, between the portions of the valve Ipng on 

 either side of this prominency. This inequality (or, in other words, this 

 eccentricity) of the keel distinguishes Mtzschia from Amphiprora, in which the 

 keel is also present ; while the presence of a keel and its accompanpng line 

 or lines of puncta, together with the absence of any form of stipes, separate 

 the present from the genus SjTiedi^a." Professor Smith, whose generic cha- 

 racter and remarks we have quoted, has brought together forms from several 

 genera, and thus has not only pointed out the remarkable character which is 

 common to them all, but also relieved those genera of members which ill 



