KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 27. N:0 3. 165 



{Frnstules with an interior skeleton , Campyloneis Geun. 

 — — : a marginal rim 4. 



— without skeleton or rim . . .... 5. 



. J Upper valve costate, eostse alternating with double rows of puiicta . . Pleuroneis Cl. 



I — — punctate-atriate . Cocconeis Cl. 



, I Lower valve with costae alternating with double rows of punota . Achnanthes Boey 



I — — ^ ecostate . . . . . . . 6. 



^ ( Upper valve costate .... . 7. 



( — ■ — not costate .... 8. 



. ( Axial area of the upper valve broad or lanceolate . . . Heteroneis Cl. 



\ — — — — — narrow or a rib . . . . . . 10. 



Eucocconeis Cl. 

 lanceolate . .... 9. 



„ I Structure: finely punctate striae . . Microneis Cl. 



" \ — coarsely punctate striae ... Achnanthidium Cl. 



..„ I Valve elliptical . . . Disconeis Cl. 



I — lanceolate or rhomboid . . . . Actinoneis Cl. 



o J Valve broadly elliptical . . 

 I — narrow, linear or lane 



Rhoicosphenia Grun. (1860). 



Valves dissimilar, strongly asymmetrical to the transverse axis, clavate. Upper valve 

 without central nodule and median line, but with an axial area. Lower valve with central nodule 

 and longitudinal line. Structure of both valves : transverse, finely punctate strise. Frustule usually 

 stipitate, cuneate, with short diaphragms at the ends. Connecting zone not complex. 



Oell-contents a single chromatophore-plate along one of the interior walls of the zone and 

 both valves, with the opening along the other wall of the zone, with slight sinuses at the base 

 and the ends, and also towards the ventral nodule; but there is no deep fissure below the median 

 line. Division of the plate as in Gomphonema (Pfitzer, Bau u. Entw. p. 91). In conjugating 

 the cells behave as Goniphonema, but when the auxopores attain to the length of the mother-cells 

 they become enclosed in a silicious, transversely costate, membrane, inside which the primordial 

 cells originate (Thwaites). 



The species which for long was the only one in this genus was in 1833 named by Kutzing 

 Gomphonema minutissimum, or G. curvatum, and was first (1860) by Gkunow removed as Ehoico- 

 sphenia curvatum to the family Achnantheae. Notwithstanding the dissimilarity of the valves 

 Bhoicosphenia bears a close resemblance to Gomphonema both in exterior and interior respects. 

 There is also some affinity to the Tabellariea, especially in the diaphragms at the ends of the 

 frustule. 



1. R. curvata Ktixz (1833). — V. clavate, with rounded, obtuse upper end, and more 

 narrow, attenuated, obtuse base. L. 0,oi5 to 0,025; B. 0,oo3 to 0,045 mm. Upper V. with narrow, 

 centrally placed axial area, and parallel striae, about 16 in 0,oi mm. Lower V. with narrow 

 or indistinct axial, and small elongated, central area. Median line with somewhat distant 

 central pores, and about 15 strise in 0,oi mm., radiate throughout and stronger in the middle. — 

 Gomphonema minutissimum Ktixz. Dec. N:o 76 (1833) according to Lagst. G. curvatum Kutz. 

 Linnaa X p. 567 PI. XVI f. 51 (1833), according to Lagst. W. Sm. B. D. p. 81 PI. XXIX 

 f. 245, 246. Bhoicosphenia curvata V. H. Syn. p. 127 PL XXVI f. 1 to 3. Gomph. marinum 

 W. Sm. B. D. I p. 81 PI. XXIX f. 246. 



Fresh and brackish water: Arctic America! Greenland! Spitsbergen! Finmark! Cape Desch- 

 neff! Behring Island! Europe generally, Baltic and Caspian seas! Atlantic coasts of Europe and 

 America! Cape Good Hope (Grun.), New Zealand (Grun.), S:t Pauls Island! Honduras (Jan. Rabh.). 



Var. major Cl. — L. 0,07; B. O.008 mm. Striae 9 in 0,oi mm. 



Fresh water: Pitt River, Oregon! 



