KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 27. N:0 3. 53 



The group most nearly connected with the Nav. Lyrates is the Nav. punctatce, both being 

 iinited by niimerous transitional forms. In some cases it is difRcult to decide whether a form 

 belongs to the Nav. punctatse or the Nav. lyratse. Such forms are for instance N. transfwja and 

 N. carinifera among the Punctatse and N Schaarschmidfii among the Lyratse. 



On the other hand the Nav. lyratpe offer some resemblance to the genus Diploneis, especially 

 in D. hyalina, D. Hudsonis and some other forms. The prolongations of the ceTitral nodule in 

 Diploneis correspond evidently to the lateral expansions of the central nodule in the Lyratfe, 

 hut there are no longitudinal lines in Lyratse as in Diploneis, and in Diploneis there is no 

 punctate space between the median line and the prolongations of the central nodule. 



All the forms of this Section live in salt water, a few only {N. pygmcea and some vaiieties 

 of N. forcipata^ living in brackish water; so that the forms of this section of Navicula are very 

 characteristic of purely marin e deposits. In the older deposits only few occur. From the Barbados 

 deposit I have seen only one specimen, of a species akin to N. Barbifoa. In the Oamaru deposit 

 there are a few peculiar forms, one of which has the terminal fissures in contrary directions, 

 and another has almost straight terminal fissures. In the deposits of the miooene or oligocene age 

 forms of Lyratse begin to become numerous, one of the most frequent being N. prcetexta. In the 

 present age, forms of this Section are very frequent, and the same species have a very wide range 

 of distribution. 



Most species of this section being transitional and their characteristics subject to great 

 variation, it is extremely difficult to construct a satisfactory artificial key. Still I believe the 

 following will be of use. 



Artificial key. 



^ j Lateral areas nniting with the central area 2. 



( — — not — — — — N. concilians 



{ 



{ 



( Central pores incrassate 6. 



'^^ I _ _ not - 7. 



f Strise abont 13 in 0,oi mm N. foreipata Grun. 



6. -I — 15 to 23 — — N. foreipata var. 



I — abont 36 — — N. pygmcea Kötz. 



N. concilians Cl. 



n ) Puncta forming straight longitndinal rows N. Durandi Kitton. 



i — — undnlating — — 3. 



„ j Lateral areas linear 4. 



broader in the middle 20. 



, ( Spaces between the areas and the median line striate 5. 



' \ — — — — — not — N. Reichardtii Grun. 



I Lateral areas shoi 



Lateral areas short, not reaching to the margin 8 



\ — — indistinct 10 



reaching — — 11. 



Striffi euding at the margin in double rows of small puncta N. rwdis Cl. 



— not — — — — — — — — 9. 



Axial area narrowed at the ends and in the middle N. abrupta, Greg. 



f Valve almost orbicular N. H. album Ci,. 



10, ■! — elliptical N. connectens Grun. 



I (N. australica A. S., N. Lyra var. atlantica, N. spectabilis, var., Rattrayi var. abbreviata). 

 _.^ I Valve indented in the middle N. distenta A. S. 



t — not — - — 12. 



..., I Valve narrow, linear with rounded ends N- Samoensis Grun. 



I — broad, elliptical to elliptic-lanceolate 13. 



..„ j Puncta of the median strise confluent towards the central nodule . . . . N. genifera A. S. 

 ■ t — — — — not 14. 



I Axial part of the valve elevated towards the ends N. Barhitos A. S. (N. Lyra. 



14. •! v. subcarinata). 



\ — — — — not 15. 



,j. ( Lateral areas very distant from the median line N. diffluens A. S. 



I''- j _ -not - - - - 16. 



