860 



SYSTEMATIC HISTOEY OF THE mEUSOEIA. 



T. Llhyca — Tetragramma Lihycum, 

 Africa. 



T. Brasiliemis (E.). — Music-like marks 



According: to Elirenberg", it 



very small 



approaches Jl musica in form. Brazil, 



Genus PLEURODESMIUM (Xlitz.). — Eriistules compressed, connected 

 in fascia-like filaments by short thread-like processes ; lateral portions 

 punctated and furnished with music-lilie marks, the hyaline central smoother 

 portion forming a band between them. 



Although Pleurodesmium was placed by Professor Kiitzing in a different 

 family from Terpsinoe, yet these genera appeared to us so closely allied that 

 we found it difficult to distinguish them, — a difficulty experienced also by 

 Mr. Tuffen West on examining an authentic specimen of Pleurodesmium 

 given us by our valued friend M. de Brebisson, which, however, was unfor- 

 tunately not in a condition to afford a satisfactory examination. 



The frustules, as in Terpsinoe, agree with the Biddulphieas in having the 

 lateral valves largely developed and entering into the front view ; they are 

 furnished with costse, enlarged at the ends and resembling notes of music. 

 M. de Brebisson thinks this genus very distinct, the frustules being connected 

 in straight series by thread-like points of attachment proceeding from the 

 furrows ; but these he informs us are very short indeed, for which reason 

 Kiitzing, like ourselves, seems to have overlooked them. 



Pleurodesmium Brehissonii (lAiitz.). 

 — Frustules contracted at their junction ; 

 costse rugose. KSA. p. 115. Cayenne. 



(vi. 23.) Lateral view oval, having 

 transverse bars and undulated sides. 



Genus EUNOTOGBAMMA (Weisse).— Front view as in Anaulus ; lateral 

 view lunate, with undulated dorsal and ventral margins. Dr. Weisse observes 

 that in the front view Eunotogramma resembles Gomphogramma, and in the 

 lateral one Eunotia (Epithemia ?). In both instances, however, the resem- 

 blance is evidently very superficial, and does not require the distinctions to 

 be pointed out. The genus doubtless belongs to the Terpsinoea3, and seems 

 to differ from Anaulus only in the lunate form of the side view. 



Eunotogramma tri- quinque- scptem- i row connecting zone, and lateral, equal, 



etnovefnloculata(Wei&se). — Lateral view stout, pinna-like septa. Lateral view 



divided by two, four, six, or eight trans- semilanceolate, constricted at each sep- 



verse septa into three, five, seven, or turn, and therefore having as many 



nine loculi. Weisse, Bulletin de I'Acad. undidations as loculi ; ends rounded, 



de St. Petersbom-g, xiii. p. 278, t. 8. f. 37. (viii. 30.) 

 Fossil. Eussia. Front view with a nar- 



FAMILY XIII.— CH^TOCEEE^. 



Frustules smooth or faintly punctated, simple or united into awned fila- 

 ments ; lateral valves, in the nonfilamentous forms, usually unequal, inflated, 

 lobed, and often furnished with bristles or other appendages ; lateral view 

 oval or circular. Marine, mostly fossil. Until Mr. Brightwell pointed out 

 their true affinity, the genera included in this group were distributed amongst 

 three families. Between Syndendrium and the Angulifereae we can perceive 

 no resemblance ; but the connexion of Chsetoceros with the Biddulphieae, and 

 the other genera with the Melosii^ece, is far more plausible. In Stephano- 

 pyxis, a true member of the latter family, the valves are crowned with 

 bristles or spines, as in some Cha^tocere^e. In Melosireae, however, aU the 

 members ought to be cj-lindrical, whereas in this family the shape, in the 

 lateral view, is much oftenor oval than circular. Although it is not difficult 

 to point out differences between the Chsotoccreae and other groups, yet, on 



