24 p. T. CLEVE, SYNOPSIS OJ' THE NAVICULOIl) DIATOMS. 



forms of Nav. Qastrum closely resemble smaller forms of Nav. peregrina var. Meniseulus, from 

 which they differ by the terminal striee being radiate throughout, but this characteristic is some- 

 times excedingly delicate. 



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

 L. 0,03 8 to 0,04 8; B. 0,oi5 to 0,02 mm. Axial area indistinct. Central area large, orbicular. 

 Striae l4 in 0,oi mm., radiate throughout, distinctly punctate (puncta about 22 in O.oi mm.) in 

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

 lept. Icon. n. PI. 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. 

 Striae 17 in 0,oi mm., very finely lineate, radiate throughout. Among the median striae 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 N. p. 55 PL II f. 29 (1867)? 



Fresh and slightly brackish water: Sweden (Lake Malaren, Gulf of Bothnia, Gotland in the 

 Baltic)! Mouth of Jenissey! Michigan! 



Var. bengalensis Grun. Ms. — Y. subrhomboidal, with broad, rounded ends. L. O.os; B. 0,oi2 

 mm. Striae distinctly punctate. 



Fresh water: Bengal (Grun.). 



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

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

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



Marine: Madagascar (Van Heurck Coll.)! 



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

 obtuse ends. L. 0,o6 to 0,o67; B. 0,oi8 to 0,02 mm. Axial area narrow; central area orbicular. 

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

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

 V. arata Gbun. F. D. Ost. Ung. p. 145 PL XXX f 58. Pant. HI 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 striae being radiate. It 

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



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

 obtuse ends. L. 0,04 to 0,045; B. 0,oi2 to 0,oi5 mm. Axial area narrow. Central area small, 

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

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

 striae are strongly radiate and finely punctate. — F. D, Ost. 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 

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



37. N. arenariaeformis Pant. (1889). — V. lanceolate, obtuse. L. 0,02; B. 0,oii mm. Axial 

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

 striae alternately longer and shorter. — Pant. II p. 42 PL VIII f. 140. 



Brackish water: Hungary, fossil (Pant.). 



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

 B. 0,0 3 mm. Axial area distinct, dilated around the central nodule. Striae 8 (middle) to 9 (ends) 



