OSTRACODA. 



115 



Though we have thought it desirable to give these brief generic diagnoses, inserting 

 only such characters as may be derived from the formation of the carapace (this being the 

 only part of the animal available to the palaeontologist) ; it should, nevertheless, be 

 clearly understood that the really important generic distinctions are, in almost all cases, 

 based upon the structure of the internal organs, chiefly, indeed, on the formation of the 

 limbs, mouth-apparatus, and sexual organs. Yet, in the majority of cases, these deep- 

 seated peculiarities coincide so remarkably with a particular form of shell that there need 

 usually be no difficulty in assigning the fossil remains met with in the Tertiary and Post- 

 tertiary strata to their proper genera. Amongst the Entomostraca of the Palaeozoic 

 formations, however, we meet with types of shell-structure far removed from those of 

 recent times and can only vaguely conjecture as to their relations. 



From the foregoing Table we have excluded altogether the family Conchoeciadae, the 

 delicate valves of which have not been found (nor, indeed, are they likely ever to be 

 found) in any geological formation. The exclusively Palaeozoic genera are also omitted, 

 as well as the recent genus Heterodesmus, which has not been met with except in the 

 Chinese seas, and seems to be allied to the Carboniferous genus Entomoconchus. 



OSTRACODA — Synopsis of Genera based upon the anatomical characters of the animal. 



I 



Possessing a bran- 

 chial appendage ; 

 palp subcorneal, in- 

 distinctly jointed, 

 ending in three 

 setae. 



Second joint of 

 lower antennae 



beai-ing a brush of setae, r well developed, terminating in two strong • * 

 Setae of the upper an- \ curved claws . . . . . . . ) •'■^ ' 



tennae very long 

 abdominal rami 



Post- 



udimentary, setiform Cypridopsis. 



without a brush of set^e. f rudimentary Potamocypri 



SetiE of the upper an- ■, -. , • j.- • ^ n 



4- „ t, i T3 i -1 well-developed, terminating m ) alike 

 tennae very short. Post- | , , j i i. ( 



abdominal rami ' strong curved claws. J) irst > 



l^and second pairs of feet j dissimilar 



Paracypris. 

 Aglaia. 



destitute of a bran- 

 chial appendage. 

 Palp 



1 . 1 • ,1 rlong, reaching beyond the apex of the ter- 7 at ^ j 



subcorneal, indistinctly I , > JSIofodromas. 



• • . -, A , £ , •' ) mmal claws. Two eyes . . . . S 

 .lomted. Sette ot lower "j 



(^altogether wanting. One eye . . . Candona. 

 f f elongated, 7-jointed, armed with long setse . Pontocypris. 



jointed 

 antennae 



distinctly 

 jointed, 

 subpedi- 

 l^form 



3-jointed ; 

 upper 

 antennae 



-{ short and robust ; 5-joiated ; in the female") 

 I shortly setose, in the male provided with a > Argillcecia. 

 l^f ew long setae . . . . . .) 



wv-'] largely developed, terminating in seve- ") p 

 lae ral long setae ) 



4-jointed ; 

 per antennae I ] 

 shortly setose. J- 



Postabdominal | rudimentary Macrocypris. 



l^rami J 



Animal unknown Goniocypris. 



* With this genus we incorporate Ci/pria (Zenker) and Chlamydotlieea (Saussure). 



