Subgenus
Tetrada (Perplana) Sidaravičiene, 1992
Selection of related publications
Nõlvak, J. 1972. A characterization of the boundary beds of the Kukruse and Idavere stages in the Lipu boring.  Loodusuurijate Seltsi Aastaraamat, pp. 39-59.   Loodusuurijate Selts. 
Sarv, L. 1959. Ordovician ostracodes in the Estonian S.S.R..  ENSV TA Geoloogia Instituudi Uurimused   IV,      1-210.
Neckaja, A. I. 1953. Tetradellidy ordovika Pribaltiki i ih stratigraficheskoe znachenie.  Trudy Vsesoûznogo Naučno-Issledovatel'skogo Geologo-Razvedočnogo Instituta (VNIGRI)         309-363.  Gostoptehizdat. 
List of species
2. Tetrada (Perplana) pabradensis Sidaravičiene, 1992 | Keila Stage
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Classification
| Organism group | Biota | 
| Kingdom | Animalia | 
| Phylum | Arthropoda | 
| Subphylum | Crustacea | 
| Superclass | Oligostraca | 
| Class | Ostracoda | 
| Subclass | Podocopa | 
| Order | Palaeocopida | 
| Suborder | Beyrichicopina | 
| Palaeocopa | |
| Family | Ctenonotellidae | 
| Genus | Tetrada | 
| Subgenus | (Neotsitrella) | 
| (Perplana) | |
| Species | bisulcata | 
| pabradensis | |
| perplana | |
| Subgenus | (Tallinnopsis) | 
| (Tetrada) | |
| Species | hibyi | 
| ventroconcava | |
| Subspecies | troppenzorum |