RECENT BRITISH OSTRACODA 



355 







Mr. D. 0. Drewett, of Jarrow. My thanks are also especially due to Dr. Baird, of tin 

 British Museum, Professor T. Rupert Jones, the Eev. Alfred Merle Norman, Dr. Alcock, 

 of Manchester, and Mr. David Robertson, of Glasgow, for much valuable advice and 

 assistance, and for the kind and liberal manner in which they have placed their colleo- 

 tions at my disposal; lastly I owe similar thanks to M. Bosquet, of Maastricht, Dr. 

 Oscar Speyer, of Hesse Cassel, and Herr G. 0. Sars, of Christiania, for the good service 

 which they have done me by the communication of their admirable memoirs and series 

 of illustrative specimens. I am fully conscious that whatever value this mono raph ma; 

 possess is owing in great measure to the generosity of these naturalists, and their kind 



interest in the progress of my work. 



The recent Ostracoda are divided by Sars into four great groups or sections, namely :- 

 (1) Podocopa, including the two families Cypridae and Cytherichn; (2) Myodocopa, 

 including the families Cypridinidse and Conchoeciadse ; (3) Cladocopa, containing onr 

 family, Polycopidse; and (4) Platycopa, containing also one family, OytherellidaB. 



The characters of these four sections may (after Sars) be stated as follows :— 



1. Podocopa.— This is by far the most extensive of the four sections, including all thi 

 freshwater, and a vast majority of the marine Ostracoda, and embracing all the forma 

 classed by the earlier writers under, the two great genera Oyprk and Cythere. The 

 lower antenna? are here simple, pediform, geniculate, armed at the apex with sharp claws, 

 and are used for swimming (as in Cypria), for walking (as in Cythere), or as prehensile 



organs. The first pair of appendages following the mouth is always a distinct maxilla 



hearing a large halfmoon-shaped branchial plate, which is bordered with nnmeron 

 ciliated setae. The next pair of appendages forms in the Cyprida, a jaw ofeomewhat 



similar shape, but in the Cytheridee becomes pediform, owing to the atrophy of the jaw 

 proper and the greater development of the palp. Of the two following pairs o «m bs 

 the last is found, in the Cypridae, to have lost its use as a locomotive organ, and is double 

 up between the valves, whilst in the Cytherid* it is used like the foregoing pjj asa 

 walking limb. The postabdomen is, in the Cytheridae, mdimentary, but n tl eCy, da 



is mostly well developed, consisting of two elongated laminar P^^ 1 ^^ 

 together^ and each armed at the extremity with two long claws. Ih ^ ^ ^ 



a -i rvup, liport is alwavs wanting the cugesiive 



often so close together as to appear single. The heart "£** "^ with tw0 



cavity has two dilatations, of which the oremost -^gT- -duced between 



lateral blind sacs. In this last family the ^^^ J idlG lit , crawling 

 the two lamina of the shell. These animals live loi tne mo i 



elv on the mud, on plants, or swimming 



throu-h the water. Their motions 



effected by the two pairs of antenna,, which move J^-^tK — 

 up and d«wn. thp lnw«r backwards and forwards, thus piopellin 



ing 



U P and down, the lower bad 

 straight line 



! lght lme * • ,i 1P forms of which the -onus Cypridma is the 



2. Myodocopa.-TIus group comprises the forms of w ^.marked dif- 



.„ xi , , . ,. i. 1,-^Lav organization ana pitw.n"- - 



Jvpe, the characters indicating a higher org_ Brancllior oda. 



fercnecs, which show an approach to the mgnei 



W antennce are here the only true ^^.^^^ 



«• the Branchiopoda) wholly lose their importance m tins respect, 



As a rnle the 



come th< 

 3 c 2 



