KoNCil,. SV. VK/r. AKADKMIKNS HAN l)LIN(iAI{. I5AN1) 26. N:i) 2. 79 



Longitudinal ril)S 2 to 4 in 0,0 1 mm 4G. 



— 5 to more — 47. 



Furrows broader in the middle D. Schmidtii Or,. 



4<> 



\ -~ not — D. Entomon Ehb. 



I Furrows l)r();ider in tlie ini<ldlt^ 48. 



\ — not — — 49. 



„ I Transverse costse (J to !l in 0,oi mm D. homboides A. S. 



' \ — — 11 — — D. divergens A. S. 



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



' \ — — 13 — — D. chinensis Cl. 



J. J Median line ending far from the margin /^>. niicrotntos Pant. 



' ( — — • — near — — rd. 



^. j Furrows abruptely dilated around the rentral nodule 52. 



■ 1 - not — — - — 53. 



Transverse cost» about 7 in 0,oi mm D. Jiyperborea Grun. 



— — — 12 — I>. vacillans A. S. 



I Furrows l)road 54. 



I — narrow bi. 



J.. J Freshwater speeies D. Jinnica Ehb. 



52. I 



55. >j 



I Freshw 



I Marine — \db. 



Longitudinal ribs few D. notabilis Grev. 



— — numerous 56. 



Central nodule small D. Grceffii Grun. 



— — large D. fusca Greg. 



Longitudinal ribs wider than the costie D. domblittensis Grun. 



— equidistant with — or closer 5!^. 



Central nodule small D. litoralis Donk. 



— large 59. 



Freshwater species (iO. 



Marine — D. cestiva Donk. 



Ribs as close as the costie D. elliptica KcTZ. 



— closer than — D. Parma Cl. 



Valve not or slightly constriifed 62. 



— constricted 74. 



Valve elliptical 63. 



— elongated with parallel or slightly concave margins 73. 



Fnrrow-s narrow 64. 



— broad 67. 



Without ocelli 65. 



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



j Furrows equally arcuate 7>. Smithii Br^b. 



(")."). ; — bent around the central nodule 66. 



I — linear D. ndvena var. recta. 



\ Central nodule large D. anbovalis Cl. 



I — — rather small D. bnreolis Grun. 



.„ j Furrows f(>rming a large, orbicular space 68. 



\ — — an elliptical or lanceolate space 69. 



j Furrows double 1). mirabilis Castr. 



' \ — single D. Platessa Cl. a. Grove. 



.f j Horns distinct 70. 



'■ ■ i — indistinct 72. 



^ j Horns divergent D. Cnnipylodiscus Deby. 



\ — approximate 71. 



_.j J Furrows broader than '.., of the breadth of the valve D. Debyi Pant. 



I — narrower D. major Cl. 



„ I Fre.shwater species D. Manleri Brun. 



\ Marine — D. nitescens Greg. 



_„ j L. 0,03 to 0,oc mm D. Szontaghii Pant. 



\ L. 0,08 to 0.24 mm D. gemmata Grev. 



56. 

 .57. 

 58. 

 59. 

 60. 

 61. 

 62. 

 63. 

 64. 



