KONGL. SV. VKT. AKAPKMIENS HANDLINGAR. HAND 26. N:() 2. 79 



.j. ( Longitudinal ribs 2 to 4 in 0,0 1 mm 46. 



' \ — — 5 to more — 47. 



) FiuTows broatler in tlie middle D. Schmidtii Ch. 



"■{ 



j Furrows 



i'"t — — r>. Enfomon Ehb. 



.^ I FuiTows broader in tbe middle 48. 



■ I — not — — 49. 



„ I Transverse costs G to i) in 0,0 1 jnm D. bomboides A. S. 



I — — 11 — — D. divcrgens A. S. 



.( (Transverse costs 9 in 0,0 1 mm J). didyma Ehb. 



I — — 13 — — D. chinensis Cl. 



P J Median line ending far from tlie margin D. microtatos Pant. 



'1 — — — near — — 51. 



i,.| I Furrows abruptelj' dilated aronnd tlie central nodule 52. 



not — — — — 53. 



äe costa about 7 in 0,oi mm D. hyperborea Geun. 



\ — — — 12 — Z>. vacillans A. S. 



P„ J Pnrrows broad 54. 



' ' ' \ — narrow 57. 



j.^^ J Fresbwater speeies B. finnica Ehb. 



\^ Marine — 55. 



gg j Longitudinal ribs few D. notabilis Gbev. 



\ — — numerous 56. 



gg J Central nodule small J5. Grceffii Gbun. 



' \ — — large D. fnsca Geeg. 



^. J Longitudinal ribs wider than the eostie D. domblittensis Grun. 



I — etjnidistant witli — or eloser 58. 



gy J Central nodule small D. litoralis Donk. 



\ — — large 5<). 



r„ j Fresbwater speeies 60. 



1 Marine — B. cestiva Donk. 



, J Ribs as close as tbe costa; B. elliptica KfJTZ. 



1 — doser than — , B. Parma Cl. 



,... j Valve not or sligbtly constricted 62. 



\ — constricted 74. 



J Valve elliptical 63. 



\ — elongated witli parallel or sligbtl.y concave margins 73. 



„„ ( Furrows narrow . 64. 



bo. > , , 



I — oroad 67. 



j ) Without ocelli 65. 



I With ocelli B. bisericita Cl. (D. Crabro var.). 



I Fnridws equally arcuate B. Smithii Bréb. 



<J5. ■• — bent around tbe central nodule 66. 



I — linear B. advena var. recta. 



.„ j Central nodule large B. stibovalis Cl. 



1 — — rather small B. borealis Geun. 



„_ j Furrows forming a large, orbicular space 68. 



\ — — an elliptical or lanceolate space 69. 



„,_. J Furrows double B. mirabilis Gaste. 



■ \ — single B. Platessa Cl. a. Geove. 



,„, I Horns distinct 70. 



o9. 



I — mdistmct ^ 72. 



_l^ ) Horns divergent B. Campylodiscns Deby. 



( — approximate 71. 



_.. J Furrows broader than '/a of tlie breailth of the valve B. Bebyi Pant. 



\ — narrower B. major Cl. 



„£, I Fresbwater speeies B. Mauleri Beun. 



\ Marine — B. nitescens Geeg. 



„., I L. 0,03 to 0,00 mm B. Szontaghii Pant. 



\ L. 0,08 to 0.24 mm B. gemmata Geev. 



