24 P. T. CLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



forms of Nav. Gastrum closely resemble smaller forms of Nav. peregrina var. Menisculus, from 

 which they differ by the terminal strise being radiate throiighout, but tliis characteristic is some- 

 times excedingly delicate. 



32. N. leptostigma Ehb. (1854). — V. elliptical, with more or less broad, rostrate ends. 

 L. 0,038 to 0,048; B. 0,oi5 to 0,02 mm. Axial area indistinct. Central area large, orbicular. 

 Strise 14 in 0,oi mm., radiate throughout, distinctly punctate (ptincta about 22 in 0,oi mm.) in 

 the middle alternately larger and shorter. — Pinmil.Jeptost, Ehb. M. Gr. XXXIII: 12 f. 25. Nav. 

 lept. Icon. n. Pl. I f. 37. 



Fresh water: Oregon, fossil! 



33. N. platystoma Ehb. (1838). — V. elliptic-lanceolate, with broad, rostrate ends. L. 0,037 

 to 0,05; B. 0,017 mm. Axial area narrow. Central area large, transversely dilated, subrhomboidal. 

 Strise 17 in 0, 01 mm., very finely lineate, radiate throughout. Among the median strise a few 

 shorter frequently occur. — Ehb. Inf. 178 Pl. XIII f. 8. M. G. XIII f. 6 b. Cl. A. D. p. 14 

 Pl. III f. 61. N. macromphala Schum. Preuss. D. II JST. p. 55 Pl. II f. 29 (1867)? 



Fresh and slightly brackish water: Swedeii (Lake Mälaren, Gulf of Bothnia, Gotland in the 

 Baltic)! Mouth of Jenissey! Michigan! 



Var. bengalensis Grun. Ms. — V. subrhomboidal, with broad, rounded ends. L. 0,o3; B. 0,oi2 

 mm. Strice distinctly punctate. 



Fresh water: Bengal (Grun.). 



34. N. OTiformis Cl. N. Sp. — V. elliptic-lanceolate. L. 0,045; B. 0,oi8 mm. Axial area 

 narrow, linear; central area large, orbicular. Strise 10 in 0, 01 mm., radiate throughout, finely 

 lineate, not alternating in length in the middle. — Pl. II f. 4. 



Marine: Madagascar (Van Heurck Coll.)! 



35. N. arata Grun. (1882). — V. lanceolate, gradually tapering from the middle to the 

 obtuse ends. L. 0,o6 to 0,o67; B. 0, 01 8 to 0, 02 mm. Axial area narrow; central area orbicular. 

 Strise 8 to 9 in 0, 01 mm. closer towards the ends, all radiate and distinctly punctate. Across the 

 strise on each side of the median line are 3 to 4 narrow longitudinal clear areas. — N. Tuscula 

 v. arata Grun. F. D. Öst. Ung. p. 145 Pl. XXX f. 58. Pant. III Pl. XXIII f. 342. 



Brackish or fresh water: Hungary, Dubravica fossil (Grun.), Hudson River (Grun.). 

 This species can scarcely be a variety of N. tuscula, the terminal strise being radiate. It 

 seems rather to belong to the group of N. Gastrum. 



36. N. Clementis Grun. (1882). — V. slightly asymmetrical, broadly lanceolate, with rostrate, 

 obtuse ends. L. 0, 04 to 0,045; B. 0,012 to 0,oi5 mm. Axial area narrow. Central area small, 

 orbicular, with 2 isolated puncta on one side of the central nodule. Strise 8 to 10 in 0,oi mm. in 

 the middle, where they are alternately longer and shorter, 16 in 0, 01 mm. towards the ends. All 

 strise are strongly radiate and finely punctate. — F. D, Öst. Ung. p. 144 PL XXX f. 52. 



Fresh water: Dubravica, Hungary, fossil! Cheshire, England (V. H. T.). 

 This species is akin to N. Placentula and at the same time to N. Demerarce of the section 

 Punctatse, the latter having also isolated puncta on the central area. 



37. N. arenariaBforniis Pant. (1889). — V. lanceolate, obtuse. L. 0,02; B. 0,oi 1 mm. Axial 

 area distinet; central area small. Strise 12,5 in O.oi mm., strongly radiate to the ends, the median 

 strise alternately longer and shorter. — Pant. II p. 42 Pl. VIII i. 140. 



Brackish water: Hungary, fos.sil (Pant.). 



38. N. ludloviana A. S. (1876). — V. lanceolate, with obtuse, subtruncate ends. L. 0,09; 

 B. 0,03 mm. Axial area distinet, dilated around the central nodule. StritB 8 (middle) to 9 (ends) 



