90 p. T. CLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



42. D. didyma Ehb. (1840). — V. slightly constricted in the middle, with tongue-shaped 

 segments. L. 0,o5 to 0,o9; B. 0,oi7 to 0,036 mm. Central nodule moderately large, its horns not 

 divergent. Furrows narrow, linear. Transverse costse 8 to 10 in 0,oi mm., crossed by numerous, 

 slightly undulating, longitudinal costse. — Pinnularia didyma Ehb. Kreideth. p. 75. Nav. didyma 

 W. Sm. B. D. XYII f. 154 a. A. S. Zeitschr. f. ges. Naturw. 1873 p. 405 PI. VI f. 1. A. S. 

 N. S. D. PL I f. 7. Atl. Xin f. 1, 2, 3. V. H. Syn. p. 90 PI. IX f. 5, 6. Suppl. B. f. 20. 

 JSf. Bombus DoNK. PI. VII f. 7 b, 8 b. 



Brackish and marine: Greenland! Spitsbergen! Kara! Finmark! Baltic (from Westerbotten 

 to Riigen), Caspian Sea (Grun.), Black Sea! Ceylon! Tahiti! Japan! Cape Horn (Petit), West Indies' 



D. didyma is a variable species, related to the var. elesdiana of D. splendida and to 

 certain forms of D. Bomhus. The outline of the valve becomes less panduriform and almost ellip- 

 tical as the water becomes less salt. The varieties in the northern part of the Bay of Bothnia 

 where the water is almost fresh are almost elliptical and closely connected with D. domblittensis. 



43. D. Bomlbus Ehb. (1844). — V. deeply constricted, with suborbicular or elliptical seg- 

 ments often of inequal size. L. 0,065 to 0,i3; B. 0,022 to 0,045; at the constr. 0,oi2 to 0,025 mm. 

 Central nodule large; its horns divergent in the middle, approximate at the ends. Furrows narrow, 

 linear. Transverse costse 5 to 8 in 0,oi mm. crossed by 2 to .5 curved, longitudinal costse. Central 

 alveoli distant from the margin. — l)ipl. Bombus Ehb. Berl. 1844 p. 84 (accord, to Chase). M. G. 

 PL XIX f 31. Nav. Bombus Greg. D. of Clyde p. 484 PL IX f. 12. Donk. B. D. p. 50 PL VII 

 f. 7 a. V. H. Syn. p. 90 Suppl. B f 22, A. S. Atl. LXIX f. 28, 29. Nav. gemina A. S. Zeitschr. 

 £ ges. Naturw. 1873 p. 405 PL VI f. 2. N. S. D. PL I f. 1, II f. 1. Atl. XIII f. 4, 5, 6, 7, 8, 9. 

 Wav. abnormis Castr. ChaU. Exp. XXVIII f. 19. 



Marine: Finmark! North Sea! Marocco! Mediterranean Sea! Adriatic! Black Sea! Caspian 

 Sea (Grun.)! Madagascar! Java! Japan! Samoa! Galapagos Islands! Cape Horn (Petit), Brazil (Atl.), 

 Florida! Campeachy Bay! Fossil: Aegina (Ehb., Atl.). 



Var. egena A. S. (1875). — L. 0,038 to O.o*:; B. 0,oi5 to 0,02; at the constr. 0,oo6 to 

 0,012 mm. Transverse costse 8 to 9 in 0,oi mm. crossed on each side of the median line by about 

 3 longitudinal costse. — Nav. gemina v. egena A. S. Atl. XIII f. 10. 



Marine: Balearic Islands! Madagascar! Manilla! China! Japan! 



Var. densestriata A. S. (1875). — L. 0,045 to 0,o56; B. 0,oi8 to 0,026; at the constr. O,oii 

 to 0,015 mm. Costse 8 to 9 in 0,oi mm. — Nav. gemina v. densestr. A. S. Atl. XIII f. 11, 12. 

 Nav. didyma A. S. Atl. LXIX f. 30. 



Marine: Marocco! Seychelles (Van Heurck Coll.)! California (Atl.). 



Var. bullata Cl. — L. 0,15; B. 0,04 7 in 0,oi mm. Horns with a row of large puncta. Costse 

 5 to 7 in 0,01 mm. 



Marine: Adriatic! Eed Sea (Deby Coll.)! California! 



44. D. Kiitzingii Grun. (1860). — V. strongly constricted, with deltoid-elliptical segments. 

 L. 0,063 to 0,15; B. 0,03 to 0,08.'i; at the constr. 0,oi4 to 0,035 mm. Horns of the central nodule 

 parallel. Transverse costse 6 to 8 in 0,oi mm., crossed by numerous (8 to 10) longitudinal, almost 

 straight or slightly undulating costse. — Nav. Kiitzingii Grun. Verb. 1860 p. 532 PL III f. 15. 

 A. S. Atl. Xni f. 22, 23, 24. Pant. I PL XXIX f 299. 



Marine: Balearic Islands! Gulf of Naples! Black Sea! Red Sea (Deby Coll.)! Cape of 

 Good Hope! Bermuda (Rae Coll.)! Valparaiso (Atl.), Galapagos Islands! Fossil: Hungary (Pant.), 

 Aegina (Atl.). 



Var. bullata Cl. — Horns with a row of large puncta. 



Marine: Gulf of Naples! Eed Sea (Deby Coll.)! 



-D. Kiitzingii is very nearly akin to D. Bombus var. densestriata, but it is larger and the 

 horns of the central nodule are parallel. 



