RECENT BRITISH OSTRACODA. 



•tail 



the eyes, the uniform white colour of the shell (except where the extremities or dorsum 

 are tinged with orange, which is not a very uncommon occurrence), lastly by t he peculiarly 

 beautiful iridescence of the shell, a character of constant occurrence in this species, but 

 never, so far as I know, found in X. aurantia; I have often observed it even in fossil spe- 

 cimens of X. depressa. The chief distinctive character of the animal it self is found in the 

 long terminal claws of the feet and lower antennae. In habitat it ranges from 2 to • '.<» 

 fathoms or upwards, while X. aurantia is purely littoral. G. 0. Sars gives the following 

 interesting account of the development of the young, which, as previon-ly stated, an 

 carried within the shell of the mother during the earlier stages of existence. " We may 

 recognize four distinct stages of development, which are often found in one and the sane 

 mother. The first stage is that of the mature egg just escaped from the ovary, in which 

 may be seen the outer membrane and an inner mass of yelk, on one side of which ia 

 visible the germinal vesicle. In the next stage the cg^ assumes a kidney-shape, om 

 side of which (the ventral) is much incurved : one already sees an indistinct appearance 

 of the eyes while there is as yet no trace of the limbs. These first appear in the third 

 stage, and first of all the lower antenna?. The valves are already form. I, and present a 

 peculiar shape, being very much produced immediately over the eyes. In the last stag, 

 the shell assumes its adult form. The antenna?, of which the upper are still only live- 

 jointed, the mandibles, and niaxillaj are already well-developed, whilst the feet are rudi- 

 mentary, and appear only as pointed inarticulate appendages." 



Genus 8. Cytheruka, G. O. Sars. 



Valves unequal and dissimilar in form, the right more or less overlapping the left on 

 the dorsal margin; surface reticulated, punctated, deeply excavated, or bearing irregu- 

 larly disposed ribs or protuberances, mostly marked with a central areola of darker colour 

 than the rest of the shell. Carapace oblong or subtriangular, the posterior extremity 

 produced into a more or less prominent beak. Hinge-processes mostly obsolete. Supe- 

 rior antenna, shortly setose, six-jointed, gradually tapering ; second joint bearing a rather 



the middle of the posterior margin ; inferior antenna, fi v,..joint«,l tenmnal 

 ellum Ion-, particulate. Mandibles robust, with very blunt teeth; palp 



seta 



short: fla ,._, 





three-jointed, branchial appendage small, and bearing only two recurved seta;. I wmwal 

 lobes of the first pair of maxilte long and narrow, "branchial plate bearing on it. ex- 

 ternal margin two non-ciliated set*, which are directed downward-, and arise from a 

 karate lobe." Feet small, the terminal claws short and enrred. Eyes distinct. Copu- 

 lative organs of the male very complex, provided with several irregular processes and 



very long spirally convoluted tube. . . „ , v iwkh 



The type of this genus, C. gMa, Midler, appears to be al tort absen from tl Br t h 

 *<**; but the genus is abundantly represented by other species, «*~»^*J 

 the smallest of all the Osiracoda, and, except 0. n, g resccns, ocenr Imost x 



**Z 7 ZZ LIT mir My Amiens (except C ^J?* 



*** J shcll-sand or from ^T^^tSiUJSS 



Process; and my sole knowledge of the anatom of the jjmjta 

 ft om the littoral species above named, which I find to correspond y 



