60 PERMIAN FOSSILS. 



General Division Entomostraca, Miiller, 1785. 



This extensive section of the Crustacea comprises several orders of aquatic 

 animals, chiefly of small size, and differing very greatly in their general appearance. 

 The orders are arranged according to the structure of the maxillary and the prehensile 

 apparatus, the characters of the pseudobranchiae, and the form of the tegumentary 

 shell or cuirass. We may notice, as representatives, the genera Branchipus, Apus, 

 Limnadia, Daphnia, Cyclops, Cypris, Cythere, Argulus, and Lernsea. The Limulus has 

 been placed by Latreille in this section ; and according to Mr. Salter, the Trilobite 

 belongs to a co-ordinate group. ^ 



Up to the present time no researches of the palaeontologist have proved the 

 existence, during the Permian epoch, of other forms of Crustacea than those 

 belonging to this division ; two genera only, Cythere, Miiller, and Dithyrocaris, 

 Scouler, have been found in the Magnesian Limestone. 



Legion Branchiopoda, Latreille. 

 Order Ostracoda, Latreille.^ 



Genus Cythere, Miiller. 



■ Synonyms. Monoculus, Aiict. -prior. 

 Cythere, Miiller, 1785. 

 Cytherina, i«»iA., 1818. 



A marine Entomostracous Crustacean. Body of animal inclosed in a bivalve 

 carapace ; animal, creeping ; provided with three pairs of feet, all protruding from the 

 shell. 



In the ' Monograph of the Entomostraca of the Cretaceous Formation,' where we have 

 entered more fully into the characters of the Ostracoda, we have subdivided the genus 

 Cythere, Miiller, into four groups, viz. Cythere proper, Cythereis, nob., Bairdia, M'Coy, 

 and Cytherella, nob., characterised by the form of the carapace and the structure of 

 its hinge. The absence of perfect valves sufficiently free from the matrix to be easily 

 examined, renders it impossible to be quite decided in the arrangement of the ten 

 Permian species of Cythere into their respective sub-genera. But taking the general 

 form as a guide, we have considered Nos. 1, 3, 4, and 5 as belonging to Cythere proper, 

 N OS. 2, 6, and 9 to Bairdia, No. 7 as a Cythereis, and Nos. 8 and 10 as Cytherella. 



These Entomostraca occur in considerable numbers in the Limestone from Byers' 

 Uuarry, referred to at page 16, both in relief on the weather-worn surface of the 



^ Geolog. Survey, 2d Decade. 



- See Jones, Monog. Entom. Cret. Form., p. 7. 



