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



The group most nearly connected with the Nav. Lyratee is the Nav. punctata, both being 

 united by numerous transitional forms. In some cases it is difficult to decide whether a form 

 belongs to the Nav. punctatas or the Nav. lyratse. Such forms are for instance N. transfuga and 

 N. carinifera among the Punctatse and K. Schaarschmidtii among the Lyratae. 



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

 in D. hyalma, D. Hudsonis and some other forms. The prolongations of the central nodule in 

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

 but there are no longitudinal lines in Lyrataj 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 {JV. pygmcea and some varieties 

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

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

 deposit I have seen only one specimen, of a species akin to N. Barbitos. 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 miocene or oligocene age 

 forms of Lyratae begin to become numerous, one of the most frequent being X. prcstexta. 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 hey. 

 Lateral areas nniting with the central area 2. 



^ ( Lateral are. 



■ \ — — not — — — — 



_ I Pancta forming straight iongitndinal rows 



' \ — — undulating — — 



Lateral areas linear 



— — broader in the middle 



N. concilians Cl. 

 N. Durandi Kitton. 

 .... 3. 



4. 



. . 20. 



, I Spaces betnreen the areas and the median line striate . . 5. 



I — — — — — not — . N. Reichardtii G-rttn. 



_ ( Central pores incrassate 6. 



^- \ _ _ not - . . 7. 



f StriaB about 13 in 0,0 1 mm. ... N. forcipata Geun. 



6. \ — 15 to 22 — — . . . . N. forcipata var. 



I — about 26 — — .... . N. pygmcea KiJTz. 



„ / Lateral areas short, not reaching to the margin 8. 



■' I — — — reaching — — . ... 11. 



I Stris ending at the margin in double rows of small puncta N. rudis Cl. 



»■ I _ not ------- - .... 9. 



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



I — — indistinct . 10. 



{Valve almost orbicular N. H. album Cl. 



— elliptical .... . . N. cormectens Geun. 



{N- australica A. S., N. Lyra var. atlantica, N. spectabilis, var., Battrayi var. abbreviata). 

 j Valve indented in the middle . .... ... . . N. distenta A. S. 



I _ not - - - ... . . . .12. 



I Valve narrow, linear with rounded ends . N. Samoensis Geun. 



\ — broad, elliptical to elliptic-lanceolate . . . 13. 



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



I — — — — not . .... . . 14. 



( Axial part of the valve elevated towards the ends . N. Barbitos A. S. (iV. Lyra. 



14. J v. subcarinata). 



I — — — — not ., 15. 



( Latei'al areas very distant from the median line N. Aifjluens A. S. 



15- •} _ -not - - - - 16. 



11. 

 12. 

 13 



