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



49. 

 50. 

 51. 

 52. 

 53. 



striae more distant than the others 50. 



not — — — C. incerta Geun. 



! 



( Median strii 



{Central area dilated to the ventral margin C. sinuata Geeg. 

 — — not — — — C. cequalis W. Sm. 



I Valve almost symmetrical .52. 



\ — decidely asymmetrical 53. 



{Central area large . C. Molleriana Grun. 

 — — small C lacustris Ag. 



Axial area narrow 54. 



moderately broad 56, 



, . ( Length about 0,os to 0,04 mm. 55. 



' \ — — 0,os to 0,07 mm C. borealis Cl. 



.p I Striae 5 in 0,0 1 mm C. alpina Grun. 



" ' \ — about 10 in 0,oi mm . C. csqualis W. Sm. 



, . f Axial area dilated to a small central area 57. 



■ I — — not — — — - 58. 



._ J Striae coarsely punctate C. Hauekii V. H. 



\ — finely — C Meinhardtii Grun. 



P„ J Length about 0,03 mm C. leptoceros Grun. 



' \ — — 0,06 mm. C. austriaca Grun. 



.„ f Median ventral striae ending in isolated puncta C. tumidula var. salinarum. 



''^- 1 - - - not 60. 



i distant from the ends ..... C. Cesatii R. 



approximate to — ... 61. 



ght, strongly excentric . 62. 



\ — — subarcuate, nearly central 63. 



I 



J' 



[ — — abruptly dilated into a central area . . 64. 



„ . ( Large. L. 0,05 to 0,i mm . . . 65. 



\ Small. L. 0,03 to 0,04 mm. 66. 



„K I Striae about 10 in 0,oi mm . C. acuta A. S. 



' \ — — 17 — — C. oregonica Cl. 



„„ I Central area rounded C. lapponica Grun. 



'I — — dilated outwards C. stauroneiformis Lagst. 



^„ I Terminal nodules distant from the ends ..... C. Cesatii Rabh. 



^^ j Median line straight, strongly excentric . 62. 



„„ I Valve broad. B. 0,02 mm . . C. Triangulum Ehb. 



narrow. B. less than 0,oi mm. . . C. hebridica Gbeg. 



„„ I Central area not dilated in the middle C. acutiuseula Cl. 



1. C. microcephala Grun. (1880). — V. almost symmetrical, linear, with rostrate-capitate 

 ends. L. 0,oi5 to 0,023; B. 0,oo3 to 0,oo4 mm. Median line almost central, straight; its central 

 pores approximate. Axial and central areas indistinct. Stx-ise 24 to 30 in 0,oi mm. almost pa- 

 rallel. — Grun. in V. H. Syn. p. 63 PL VIII f. 36 to 39. C. minuscula A. S. Atl. IX f. 58 to 61? 



Fresh water: Greenland! Scotland! Sweden (Vernamo, fossil)! Belgium (V. H.), Ecuador, Bancs! 



2. C. (Encyonema) Cesatii Eabh. (1853). — V. nearly symmetrical, narrow lanceolate, 

 gradually tapering from the middle to the acute ends. L. 0,045 to 0,0.5; B. 0,oo6 to 0,oo7 mm. 

 Median line almost central, with approximate central pores and slightly curved terminal fissures 

 at some distance from the ends. Axial area narrow; central area small. Strise radiate throughout, 

 about 19 in 0,oi mm., very finely punctate. — Nav. appendiculata Grun. Verb. 1860 p. 552 PL IV 

 f. 29. Nav. Cesatii Rabh. Siissw. D. p. 39 PL VI f. 89. V. H. Syn. p. 88 PL VIII f. 35. Cym- 

 hella Cesatii .Grun. A. S. Atl. LXXI f. 48, 49. 



Fresh water: Greenland! Iceland! Swedish and Russian Lappland! Scotland! Sweden (We- 

 nern)! Belgium (V. H.), Piedmont (Rabh.), Canada! 



This form, easily recognized by the distance of its terminal nodules from the ends of the 

 valve, is so slightly asymmetrical, that one might regard it as a Navieula. It seems to be an in- 

 habitant principally of northern or alpine regions. In Verb. 1860 (p. 571 PL VII f. 16) Grunow 

 mentions a Colletonema dubium as occurring together with C. Cesatii (his Nav. appendiculata) and 



