KONGL. SV. VKT. AKADEMIENS HANDLTNGAR. BAND 26. N:0 2. 



79 



45. 

 46. 

 47. 

 48. 

 49. 

 50. 

 51. 

 52. 

 53.. 

 54. 

 55. 

 56, 

 57. 

 58. 

 59. 

 60. 

 61. 

 62. 

 63. 

 64. 



65. 



66. 

 67. 

 68. 

 69. 

 70. 

 71. 

 72. 

 73. 



/ Longitndinal ribs 2 to 4 in 0,0 1 

 \ — — 5 to more — 



Furrows broader in the middle 



— not — — 



Furrows broader in the middle 

 not — — 



j Furro' 



46. 



47. 



D. Schmidtii Cl. 

 D. Entomon Ehb. 



. . 48. 

 49. 



I Transverse costse 6 to 9 in 0,oi mm D. bomboides A. S. 



\ — — 11 — — . . . D. divergens A. S. 



j Transverse costse 9 in 0,oi mm . . . D. didyma Ehb. 



\ — — 13 — — . . . D. chinensis Cl. 



( Median line ending far from the margin . . D. microtatos Pant. 



— near — — . . . . 51. 



Furrows abruptely dilated around the central nodule 52. 



not — — — — . 53. 



I Furro 



(Transverse costa about 7 in 0,oi mm 

 - _ _ 12 - 

 {Farrows broad ... 

 — narrow . 

 j Freshwater species . 

 \ Marine — 



{Longitudinal ribs few 

 — ■ — numerous 

 / Central nodule small . 



\ — — large 



J Longitudinal ribs wider than the costse 



\ — equidistant with 



j Central nodule small . . . 



\ — — large ... 



/ Freshwater species . 



1 Marine — . . 



j Ribs as close as the costs 



\ — closer than — 



J Valve not or slightly constricted 



\ — constricted 



— or closer 



D 



D. hyperborea Geun. 

 . I), vacillans A. S. 

 54. 

 . . 57. 



D. finnica Ehb. 

 .... 55. 

 D. notabilis Gbbv. 



... 56. 

 . D. Grwffii Getjn. 

 D. fxisca Geeg. 

 domblittensis Geun. 

 ... .58. 

 D. Utoralis Donk. 

 . . .59. 



60. 



D. cestiva Donk. 

 . D. elliptiea Kutz. 

 . . D. Parma Cl. 

 . . . 62. 



74. 

 63. 

 73. 

 64. 

 67. 



Valve elliptical ... 



— ■ elongated with parallel or slightly concave margins . ... ... 



Furrows narrow ... 



— broad . . . .... 



Without ocelli 65. 



With ocelli . . . D. biseriata Cl. (D. Crabro var.). 



Furrows equally arcuate D. Smithii Bbj^b. 



— bent around the central nodule . . . 66. 



— linear ... D. advena var. recta. 



j Central nodule large .... D. subovalis Cl. 



\ — — rather small . . . . . D. borealis Gbun. 



( Furrows forming a large, orbicular space 68. 



\ — — an elliptical or lanceolate space 69. 



( Furrows doable D. mirabilis Caste. 



\ — single D. Platessa Cl. a. Gbove. 



{Horns distinct 70. 

 — indistinct .72. 



j Horns divergent D- Campylodiscus Dbby. 



( — approximate 71. 



( Furrows broader than Va of the breadth of the valve D. Debyi Pant. 



\ — narrower D. major Cl. 



J Freshwater species .... ...... ... D. Maiileri Beun. 



\ Marine — .... . . . . . . . D. nitescens Geeg. 



( L. 0,03 to 0,06 mm D. Szontaghii Pant. 



\ L. 0,08 to 0,24 mm . D. gemmata Gkev. 



