# 



RECENT BRITISH OSTRACODA. 439 



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 the 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 itself is found in the 

 long terminal claws of the feet and lower antennae. In habitat it ranges from 2 to 60 

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

 interesting account of the development of the young, which, as previously stated, are 

 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 same 

 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 is 

 visible the germinal vesicle. In the next stage the egg assumes a kidney-shape, one 

 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 antennse. The valves are already formed, and present a 

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

 the shell assumes its adult form. The antennae, of which the upper are still only five- 

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

 mentary, and appear only as pointed inarticulate appendages." 



Genus 8. Cytherura, 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 antennae shortly setose, six -jointed, gradually tapering ; second joint bearing a rather 

 long seta on the middle of the posterior margin ; inferior antenna; five-jointed, terminal 

 claws short ; flagellum long, triarticulate. Mandibles robust, with very blunt teeth; " palp 

 three-jointed, branchial appendage small, and bearing only two recurved setse." Terminal 

 lobes of the first pair of maxillse long and narrow, " branchial plate bearing on its ex- 

 ternal margin two non-ciliated setae, which are directed downwards, and arise from a 

 separate lobe." Peet small, the terminal claws short and curved. Eyes distinct. Copu- 

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

 very long spirally convoluted tube. 



The type of this genus, C. gihba^ Miiller, appears to be almost absent from the Britisli 

 shores ; but the genus is abundantly represented by other species, sixteen in all. They 

 are the smallest of all the Ostracoda, and, except C. nigrescens, occur almost ex- 

 clusively beyond low-water mark. My specimens (except C. nigrescetis) have been 

 picked from shell-sand or from dredged mud which has been subjected to a drying- 

 process ; and my sole knowledge of the anatomy of the genus has therefore been derived 

 from the littoral species above named, which I fie d to correspond very accurately with 



