784 SYSTEMATIC HISTORY OF THE rNTrSORIA. 



means a satisfactory group, and we Believe that Sjiiedi-a and the other genera 

 Avith wand-like frustiiles should be removed from this family, whether they 

 be united to the Fragilarieae or retained together as a distinct family ; but the 

 object of tliis work is rather to present an ej^itome of what has already been 

 done than to introduce any extensive alterations. " The genus Campylo- 

 disciis is near to the ]Melosii^ea3, but the disk is not circular but elliptical. 

 Siuii'ella and the free frustiiles of Sjmedra are related to the K'aviculese, but 

 they want the middle clearly- defined nodule in the secondary sides. Bacil- 

 laria is closely allied to the Fragilariea), especially to Diatoma ; but the striae 

 of the friistule are interrupted in the middle, while in Diatoma they are 



pervious Comparing together the genera Campylodiscus, tSurii'ella, Bacil- 



laria, Synedra, it is easily perceived that the last two only deviate from the 

 Fragilarieae by the character of interrupted strise ; and the first two, deviating 

 sensibly in the succession of species from the cii^cular shape of the lateral 

 sinfaces, or of the transverse section, establish a transition between the 

 Melosii^ese, and the group formed of these two genera, along with the Fra- 

 gilarieae and the Meridiete. Hence it is impossible to establish an organo- 

 graphieal character that shall embrace the entire family and strictly represent 

 its type." (Meneg.) 



Genus BACILLARIA (Gmel.). — Frustules linear, straight, united into a 

 short band, moving on each other by a sliding motion without separation ; 

 valves haA-ing a longitudinal punctated keel. The elongated wand-like fms- 

 tiiles distinguish this from all other genera, except some species of Diatoma 

 and Synedi-a. It differs from the former by the frustules not forming zigzag 

 chains, and from the latter by its band-hke filaments. " The principal organo- 

 graphical character that distinguishes Bacillaria from the Fragilarieae is the 

 same that allies it to a different group of the family, viz. the interruption of 

 the transverse striae in the median hue of the secondary siufaces, to which is 

 added the parallelism of the primary siufaces." (Menegh.) 



* Frustules united into a short hand l^te, hvaline ; striae obsolete. "" 



Bacillaria paracloxa (Gmel.). — 

 Valves linear lanceolate, E Inf. p. 195 ; 

 SBD. pi. 32. f. 279. Ditches in salt 

 marshes. Em-ope. (iv. 18 ; ix. 166, 

 167.) 



2 * Frustules bundled. 



B. cursoria (Donkin). — Valves lanceo- 



TMS. vi. p. 16, pi. 3. f. 12. Marine. 

 England, (iv. 19.) 



B. socialis (Greg.). — Valves lanceolate, 

 with fine, but distinct, transverse striaD. 

 = Nitzschia socialis, Greg. TMS. v. p. 8, 

 pi. 1. f. 45. Marine. Scotland. Frustules 

 in groups, striae 30 to 36 in -001. Greg. 



Genus HOMCEOCLADIA (Ag.). — Frustules bacillar, Nitzschoid, within 

 subular, siibmembranaceous, branched filaments. Thj frustules are usually 

 fasciculated ; and their structure, which is that of the genus Mtzschia, sepa- 

 rates the present from the other frondose genera (Sm.). When dried, the 

 filaments become opake, and usually acquire a metallic lustre. 



HoMCEOCLADiA Murtiana (Ag.). — H. Ancjlica (Ps.^.). — Frond trichoto- 

 Frond umbellately branched, membrana- moiis below, dichotomoiis above, opake 

 ceous, rugose, opake when dried; frustules when dry, scarcely rugose ; frustules very 

 crowded, linear, elono-ated, obtuse. Ag. long, linear, obtuse. Ag CD. p. 25 ; KB. 

 CD. p. 25 ; KB. p. 110, t. 30. f 83. =^. j t. 30. f. 82. France and England. Does 

 Anglica, Ptalfs, Annals, xvi. pi. 3. f 1. i not adhere to paper. We are unable to 

 Marine. Europe, (iv. 2,3; xi v. 47-49.) determine from the fragments we have 

 Fronds much branched, flaccid when re- { examined whether this is truly distinct 

 cent, and of a dark olive-colour, -^dth a ' from H. 3Iartiana. 

 metallic lustre and transversely wi-inkled H. Arhuscula (K.).— Very much and 

 when dried. umbellately branched, upper branches 



