OF THE STRIATELLEJE. 803 



FAMILY YI.— STRIATELLE^. 



Filaments compressed ; the central portion of the frustiile furnished mth 

 incomplete longitudinal septa, which appear like stri« or costaB. The Stria- 

 tellese form a verv distinct grouj), distinguished from every other by having 

 parallel longitudinal striae or costae on the central or connecting portion of the 

 frustule. " The appearance of longitudinal striae is in fact produced by 

 siliceous plates arising internally from the margins of the filament, and ex- 

 tending towards but not reaching the centre. The interior is thus divided 

 into chambers, opening into a central space. When viewed laterally, this 

 central space resembles a canal, especially as the inner edge of each plate has 

 a concave outline " (Ealfs, ANH. xiii.). The striae and septa are frequently 

 conterminal ; in some genera this appearance is constant, and then the striae 

 are said to be interrupted. We beheve, however, that the striae are really 

 continuous, although always more strongly marked where they coincide with 

 the septa, and, on the other hand, very indistinct, especially in a young state, 

 when they are merely formed by an internal rib. Prof. Smith adds the 

 following explanation : — " The valves (lateral surfaces) are similar in character 

 to those of the other Diatomaceae, and are formed dui^ing self-division in the 

 same manner ; but, instead of the usual repetition of the process of valve- 

 formation, we are here presented with a subsequent intervalvular development 

 which, not confined to the exterior of the frustule, projects a plate of silex 

 into its interior, forming a septum or partition extending towards, but not 

 reaching, the centre of the cell, and appearing as a compressed rim or annulus 

 of silex, whose outer or larger cii'cumference follows the exterior outline of 

 the frustule, and whose inner edge bounds the free space which serves as a 

 channel of commimication between the chambers into which the cell is thus 

 divided. This process is either simultaneous, and the frustule definite, or 

 successive, and the frustule indefinite. In the fii\st case the annuli of silex 

 are formed during the production of the valves in the progress of seK-division, 

 and on every repetition of such production ; while in the second case the 

 formation of the annidi is continued after the production of the valves, and 

 is repeated an uncertain number of times before the recurrence of a new 

 valve-production " (BD. ii. p. 32). 



Kiitzing divides this group into Striatelleae and Tabellarieae, but we agree 

 with Meneghini in thinking this di\T.sion unadvisable. ^'Any one," says the 

 latter, " examining these beings with diligence, will entirely convince himself 

 that the distinction of the two orders is altogether insufficient. No Tabellaria 

 has a central nodule in the secondaiy surfaces at all to be compared with 

 that of the Diatomeae constituting his order Stomaticae in his first tribe. I 

 fii^mly believe that Tabellarieae and Striatelleae ought to constitute one family, 

 since the diaphragms, which are considered characteristic of the second ex- 

 clusively, are not wanting in the first" (M. I. c. p. 475). 



Genus STRIATELLA (Ag., K.).— Filament of few fnistules ; stipes long; 

 frustules longitudinally striated, laterally lanceolate, with a median line ; 

 septa short, inner ones longest. Marine. The long stipes and absence of 

 transverse striae on the central portion best distinguish this genus. 



^TmATB-Li,Aiimptmctata(Ljngb.,Ag.). 

 — Frustules hyaline, subquadrate, with 

 numerous fine, parallel, continuous lines ; 

 stipes longer than the fi-ustule. SBD. 



ii. p. 37, pi. 39. f. 307. Not uncommon ^ _ . 



in the autumn on Zosteraand the smaller ' roundish central mass. (iv. 40.) 



3r2 



Algse. Filaments minute, pale yellowash- 

 brown, glass-like, and glittering, usually 

 composed of few frustules. The septa 

 are very short. The internal colouring 

 matter is generally collected into a 



