or THE CHiET0CEREJ3. 861 



account of the variety in theu^ forms, we confess oiu' inability, in the present 

 state of oiu- knowledge, to give a concise definition which shall include its 

 own members and exclude all others. We shall therefore content oui'selves 

 with pointing out those characters which will enable us to recognize mth 

 tolerable certainty those Diatoms which belong to it. The filamentous species 

 diff'er by their awns so much from every other genus that they cannot be 

 mistaken. Mr. Brightwell, in his excellent paper on Chaitoceros, regards 

 this as the typal state: he says, "A careful examination of most of the 

 species of Cha^toceros and other allied genera, described by Ehrenberg as 

 found ui a fossil state, have satisfied us that most, if not all these, will, when 

 found in a li\ing state, turn out to belong to the singular filamentous and 

 horned group which may for the present be comprehended in the genus 

 Chaetoceros." Those forms also which have dissimilar-shaped valves, espe- 

 cially when lobed or hirsute, may be safely placed here ; and it is very pro- 

 bable that some species with imequal valves, still retained in Melosireae, 

 might likewise be included with propriety. 



The genera themselves are by no means firmly established ; for, as Mr. 

 Brightwell observes, " most of the described species have been found only in 

 a fossil, or rather, if we may so term it, a deposit state ; and in this state it 

 is clearly difiicult to form a correct idea of either species or genera, since 

 deposits give no information as to the Diatoms being in threads or solitary 

 frustules." We shall not attemj)t to reconstruct the genera, for to do so 

 prematurely would only increase the difficulty and cause confusion; for 

 " much must yet be brought to light before a satisfactory classification of this 

 group can be eff'ected " (Brightwell). Although only a few species have as 

 yet been gathered in a hving state, yet, as most of them are found in guano, 

 it is probable that nearly all still exist ; and when their habits are better 

 known, we may fairly expect to obtain them. They seem to inhabit deep 

 water, as Mr. Norman has met with them, more than once, in the stomachs 

 of Ascidiae from such situations. 



Genus CH^TOCEBOS (Ehr.).— Frustules without stride, united with the 

 adjacent ones by the interlacing on each side of awns proceeding from the 

 fiaistulc or from a cingulum between the frustules, and so forming a filament. 

 The filaments are imperfectly silicious and very fragile. The awns are tubular, 

 sometimes spinous or serrated, and often of great length, though, according 

 to Kiitzing, short in an early state. Klitzing defines the genus as follows : — 

 '' Frustules concatenated, equally bivalved, turgid, with two apertures on 

 each side, which at the earliest period are very shortly tubular and the cor- 

 puscles contiguous, afterwards longly awned and the corpuscles distant." 

 If the awns be overlooked or broken off", the frustules may be mistaken for 

 species of Melosira. No person who wishes to study this beautiful but diffi- 

 cult genus should fail to obtain Mr. Brightwell's valuable paper on it in the 

 Journal of ISIicroscopic Science. 



^-r,^, - 1 ^ 1 ■ ,-,■,,] species" CBai. mlit.). In the fi-ont view 



* i^r^.s^«/..,i^/.^^.r«/r?.t^,m^^rid.^a^' j[^ frustules are linear, three or four 



t/w mickUe. | ^^^^^^ ^s long as broad, ^^Aih. stout awns 



Ch^toceros Diploneis (E.). — Frus- | arising from the angles. Lateral view 

 tules in lateral view panduriform, in i pandiiriform, with rounded ends. 



front view linear ; a-wnis smooth. KSA 

 p. 138 ; EM. pi. 33. 18. f. 1 -, Bai. in Amer. 

 Journ. of Science, xlviii. pi. 4. f. 19 (la- 

 teral view). = C. Bacillaria, Bai. /. c.i. 18 

 (front view). Bermuda deposit. " ChcB- 

 toceros Diploncis and C. Bacillaria are 



2 * Frustules laterally oval or circular ; 

 atvns spinous. 



C. 5ore«/e(BaLl.), — Frustules quadrate ; 

 a\NTis very long, spinous, arising from 

 the inner surface, not from the angles. 



merely different positions of the same ' BC. 1854, pi, 7. f 22, 23 ; Bri JjVIS. iv 



