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Coscinodisceae. 
A - Frustula tympanoidea valvis plerumque menisciformibus vel cu- 
pulatis 
a valvae paulo convexae, subtiliter et radiatim granulatae, granulis 
centro rarioribus Antelminellia Schùtt 
b valvae paulo convexae, subtiliter granulatae, granulis radiantibus 
aequa manu per totam superficiem distributis, spinulis brevis- 
simis submarginalibus ornatae Ethmodiscus Castrac. 
c valvae valde convexae, usque hemisphaericae vel subconicae, 
grosse granulatae vel cellulosae centro depressae hyalinae vel 
subtilissime punctatae Porodiscus Grev. 
B - Frustula discoidea valvis complanatis vel inflatis vel depressis, 
exceptione cupulatis 
a frustula radiis membrana inter se coalitis margine valvarum juxta 
zonam connectivam insertis ornata 
Planktoniella Schùtt (incl. Valdivieìla Schimp.) 
b frustula discoidea orbicularia, exceptione elliptica, elongata aut 
lanceolata, valvis per totam superficiem aequa manu granulatis 
vel cellulosis interdum rarius spinulis laxe et symmetrice di- 
spositi margine ornatis 
a valvae circulares, exceptione ellipticae, elongatae vel lanceolatae 
structurà cellulosa vel punctulatà, frustulis solitariis an gemi- 
nati Coscinodìcus (Ehr.) Ratt. 
p valvae circulares punctis laxe dispositis notatae, frustula solita- 
ria vel geminata in seriem filamento uno per porum centralem 
coalita; spinis in valva peripherice insertis, ex his saepius una 
ceteris majore Thalassiosira Cl. 
y valvae circulares punctulatae, pseudonodulo parvulo et spinis 
periphericis ornatae; frustula solitaria vel geminata in seriem 
filamenti compluribus per poros congruentes consociata, inter- 
dum involucro gelineo circumfusa Coscinosira Gran 
6 frustula solitaria vel geminata in familias magnas sphaericas 
involucro gelineo coalita invicem filamenti debilibus gelineis 
consociata; valvis circularibus laxe punctulatis, pseudonodulo 
parvulo spinulisque periphericis ornatis, subtiliter striolatis 
Cyclosira H. Per. 
