KONGL. SV. VET. AKADEMIENS HANDLINGAK. BAND. 18. N:() 5. 13 



N. subdivisa GrUN. (Nordsee Diat. fig, 20). 

 N. eonsimUis A. Schm. (1. c. p. 46). 



N. cemula GuuN. (in A. Schm. Nordsee Diat. II, fig. 47). 



N. superimposita A. Schm. (Nordsee Diat. II, fig. 34 and Diat. Atl. PI. 46, 

 fig. 61). 

 To these species are two undescribed forms nearly allied: N. Bruchii Grun. 

 and N. multiseriata Grun. 



N. Bruchii Grun. (PI. III. fig. 35, ""7,) found on Tahiti, is in length 0,04 mm. 

 and in breadth 0,012 mm. 



jV. multiseriata Grun. (PI. Ill, fig. 36, """/i) from Tongatabu, is in length 0,036. 



Navicula. Section: Pseudo-amphiprora Cl. 



I propose to include in this section a small number of Navicula-forms, which 

 are in some respects akin to Araphiprora and in other to Stauroneis. The valve on 

 both sides in the median line is divided by a keel into two portions. The central no- 

 dule is transversely dilated into a short stauros, reaching the above named keels. The 

 type of the section is: 



Navicula arctica Cl. 



In my paper On the arctic Diat. (Bih. till K. Sv. Vet. Ak. Handl. 1873, 1, 

 N:o 13, p. 16, PL III, fig. 13). 



This fine species was first described and somewhat indifferently figured by Bailay 

 (Smiths. Contr. Vol. VII, p. 8. fig. 14 and 15, 1853) as Amphora stauroptera. Gre- 

 gory afterwards gave (in his Diat. of Clyde 1857, p. 34, PI. IV, fig. 59 c.) a very fine 

 figure of the species in (|uestion in S. V., but he regardes it as Anqjhiprora lepidoptera. 

 At the same time he describes the F. V. as Amph. obtusa (fig. 60 1. c). but Mr. Lager- 

 STEDT (Bih. till K. Sv. Vet. Ak. Handl. T. Ill, N:o 15, p. 46) has found that the two 

 figures (59 and 60) belong to the same species. As the names N. stauroptera and N. 

 obtusa have been used for other forms it will be most conveniant to name the species 

 N. arctica. A. Schmidt has figured the species in his Nordsee Diat. PL III, fig. 1 as 

 Amp)hiprora obtusa Greg. If the Nav. arctica O'Meaka (Micr. Journ. Vol. XIV, PL 

 VIII, fig. 1) belongs to this species I d'ont know. 



The Nav. arctica lives in the northern part of the Atlantic. It has been issued 

 in Cl. et Moll. Diat. N:o 57. 



21. Navicula jugata Cl. 



Elegantly elliptic with parallel, indistinct, and punctate stria;, 10 in 0,01 mm., 

 between the keels and the margins. The median portion of the valve, between the 

 keels, seems in very oblique light and with good objectives to be exceedingly finely 

 striate. 



