On the Classification of the Diatomacese. By M. Paul Petit. 77 
undulate. It is rather an abnormal or distorted condition of 
N. sigmoidea than a true variety. I have seen N. scalaris and 
JSf. spectabilis Ehr. contorted in a precisely similar manner to the 
French form : the undulations are very irregular; in some specimens 
they appear on one -half of the valve only, on others they are 
central. — F. K.] 
EXPLANATION OF PLATES CLXXXVII., CLXXXVIII. 
Plate CLXXXVII. 
Fig. 1. — Cocconeis pcdiculus Ehr. a, s. v. ; 6, f. v. 
„ 2. — Achnanthes exilis Kg. 
„ 3. — Gomphonema constrictum Ehr. a, b, f. v. ; c, s. v. 
„ 4. — Schematic section of a Gomphonema (after Borscow). 
„ 5. — „ „ Cymbella (after Pfitzer). 
„ 6. — Cocconema cyinbiforme Ehr. a, s. v. ; b, f. v. 
„ 7. — Navicula viridis Bab. a, s. v. ; b, s. v. 
„ 8. — Schematic section of Navicula. 
„ 9. — „ „ Amphipleura pellucida Kg. (after Borscow). 
„ 10. — „ „ Amphiprora Baltica Pfitz. (after Pfitzer). 
„ 11. — „ „ Nitzschia palea Kg. (after Borscow). 
„ 12. — „ „ N. amphioxys Sm. (after Borscow). 
„ 13. — „ „ N. linearis Sm. 
,, 14. — Nitzschia acicularis Kg. (after de Brebisson MSS.). 
„ 15. — N. linearis Wm. Sm. a, s. v. ; b, f. v. 
„ 16. — Schematic section of Surirella ovdis (de Brebisson MSS.). 
„ 17. — Cymatopleura solea W. Sm. a, s. v. ; 6, f. v. 
„ 18. — Synedra splendens Kg. a, s. v. ; 6, f. v. 
„ 19. — Schematic section of a Synedra. 
„ 20. — Himantidium pectinale Kg. a, s. v. ; 6, f. v. (after de Bre- 
bisson MSS.). 
„ 21. — Diatoma vulgare. a, s. v. ; 6, f. v. 
„ 22. — Meridian circulare Ralfs. a, s. v. ; 6, f. v. 
„ 23. — Podosphenia Lyngbyei Kg. (after de BreTfisson MSS.). 
„ 24. — Grammatophora marina Kg. (after \V. Smith). 
„ 25. — Striatella unipunctata Lyrig. 
„ 26. — Amphitetras antediluviana Ehr. (after W. Smith). 
„ 27. — Coscinodiscus centralis Ehr. (after Schultze, ‘ Q. M. J.’ vol. v. 
1859). 
„ 28. — Cyclotella operculata Kg. a , s. v. ; 6, f. v. 
„ 29. — Melosira varians Ag. 
„ 30. — Amphiprora paludosa W. Sm. (after W. Smith). 
Plate CLXXXVIII. 
Fig. 1. — a, b, Navicula firma Kg., var. scolioplenroides, nov. var. ; c, ditto. 
„ 2. — o, 6, Cymbella turgida Greg., var. excisa, nov. var. 
„ 3. — a, b, Stauroneis Cohnii Hilse. 
„ 4 . — Surirella patella Kg. 
„ 5 . — Campylodiscus noricus Ehr., var. &. costatus forma. 
„ 6 . — Nitzschia sigmoidea Nitz., var. undulata, nov. var. 
All the figures on this plate are enlarged 600 diameters. 
Correction to previous paper. 
Page 10, line 13 from top, insert bracket after “Ralfs.” 
