122 p. T. cleve, synopsis op the naviculoid diatoms. 



the latter genus much larger. Several species of Frustulia (as F. vulgaris) live enclosed in gela- 

 tinous tubes and have been considered as belonging to a separate genus (Colletonema Thaw.); 

 others live in gelatinous masses {Frustulia Ag., Ehb., KCtz.). No generic distinctions may be 

 founded on such characteristics. Br^bisson founded 1868 (Ann. de la Soc. phytol. et microsc. de 

 Belgique, Vol. I p. 201) the genus Van HeurcJcia on the peculiar structure of the central nodule 

 and the median line. With Peitzer I am inclined to retain the old name Frustulia. 



Artificial key. 



^ (Valve rhomboid to lanceolate . . . . ,3. 



\ — linear to elliptic-linear . ... . 4. 



„ f Size small. L. 0,028 to 0,03 mm. . . . F. styriaca Gbun. 



\ — larger. L. 0,05 or more . . . . . . 3. 



g j Median striae slightly radiate . . ... . . ■ ■ F. vulgaris Thw. 



\ — — parallel . . . . ... . F. rhomboides Ehb. 



Terminal nodules near the margin . . F. interposita Lewis. 



distant from — . . F. Lewisiana Geev. 



J Terminal nodul 



1. F. styriaca Grun. (1880). — Y. narrow rhombic-lanceolate. L. 0,o28 to 0,o3; B. 0,oo5 

 to 0,006 mm. Central nodule elongated. Strise slightly radiate, also at the ends, about 24 (middle) 

 to 27 (ends) in 0,oi mm. — Nav. (Vanheurchia?) styriaca GtRun. V. H. Syn. Pi. XVII f. 7, 8. 



Fresh v^ater? 



I have not seen this species, which has the appearance of a small F. rhomboides. 



2. F. vulgaris Thw. (1847). — V. narrow-lanceolate, with subrostrate, obtuse ends. L. 

 0,05 — 0,07; B. 0,011 mm. Central nodule elongated. Striae 24 (middle) to 34 (ends) in 0,oi mm., 

 slightly radiate in the middle, transverse at the ends. Frustules enclosed in unbranched gelatinous 

 tubes. — Colletenema vulgaris Thw. Ann. N. H. (2) I Pi. XII f. 4. W. Sm. B. D. II p. 70 PL 

 LVI f. 351. GrRUN. Banka D. II f. 15. Nav. dirhynchus Donk. B. D. PL V f . 3 (1871) Ehb.? 

 Kiitz? Vanheurchia vulgaris V. H. Syn. p. 112 PL XVII f. 6. 



Fresh water: Sweden! Norway! Finland! Saxony! Belgium (V. H.), Switzerland (Brun.), 

 Siberia! Japan! Bengal! Australia (Orara River, Blue mountains etc.)! Tasmania! Ecuador! 



Var. asymmetrica Cl. — Y. elliptical, asymmetrical, with obtuse ends. Median line excen- 

 tric, more approximate to the less convex margin. Terminal nodules at some distance from the 

 ends of the valve. Striae 22 to 30 in 0,oi mm., somewhat radiate in the middle and closer at 

 the ends, punctate; puncta arranged in longitudinal undulating rows, 19 to 23 in 0,oi mm. — 

 PL V f. 29. 



Brackish water: Sierra Leone! Cameroon! Tasmania! Newark N. Jers. fossil (Champlain epoch)! 



3. F. rhomboides Ehb. (1843). — V. rhombic-lanceolate, with obtuse ends. L. 0,o7 toO,i6; 

 B. 0,015 to 0,03 mm. Central nodule small or elongated. Transverse striae parallel, 23 to 24 in 

 0,01 mm.; longitudinal striae 20 to 25 in 0,oi mm. — Nav. rhomboides Ehb. Am. Ill: i f. 15? 

 W. Sm. B. D. I PL XVI f. 129. Grdn. Banka D. PL II f. 14. Vanheurchia rhomb. Breb. Ann. 

 Soc. phyto. et micr. de Belgique Vol. I p. 204 (1868). V. H. Syn. p. 112 PL XVII f. 1, 2. 



Fresh water: Sweden! Finland (from Russian Lapland to Abo)! England! Belgium (V. H.), 

 Bengal! Australia (Daintree River, Blue Mountains)! New Zealand! Greenland! Canada! Sierra 

 Nevada! White Mountains! Demerara River! Brazil! 



Var. lineolata Ehb. (1843). — V. with several coarse longitudinal furrows. — N. lineolata 

 Ehb. Am. PL I: s f. 4 a? M. G. PL XVI: i f. 3 etc. 



Fresh water: Sweden (Degemas, fossil)! Bengal! New Zealand, fossil! 



Var. oregonica Cl. — V. narrow. L. 0,i; B. 0,oi5 mm. Transverse striae 30, longitudinal 

 25 in 0,01 mm. 



Fresh water: Oregon, fossil! 



