A Synopsis of the Recent British Ostracoda. 121 



but it happens that some species which are common enough 

 in the British seas, though unknown to Sars when his 

 memoir was written, are exactly intermediate in character, 

 presenting different combinations of those peculiarities which 

 were relied on to separate Cy there from Cythereis. It is there- 

 fore necessary either to constitute two or three new genera for 

 the reception of these aberrant forms, or to give a more ex- 

 tended signification to the original genus, so as to include all 

 under the one term Cythere. The latter is the course which I 

 have adopted. The intermediate species here referred to are 

 C. albomaculata, convexa, and rubida. 0. convexa exhibits a 

 remarkable approach to the genus Bairdia in general outline, 

 the two valves being very unequal and decidedly beaked behind. 

 In all essential points, however, it is a true Cythere. This 

 genus includes a very large proportion of the fossil species ; its 

 preponderance appears, indeed, to have been greater during 

 the earlier periods of the earth's history than now, though 

 possibly this may partly arise from the great thickness and 

 durability of the shells of many species, and especially of many 

 of the fossil forms which have thus been preserved, while other 

 more fragile species may have been destroyed. 



The Cytheres have no power of swimming, and are met 

 with abundantly both amongst the fuci of the littoral zone and 

 amongst the mud and sand of the deep-sea bed. A muslin 

 or crinoline net used amongst the rock-pools of any part of our 

 coast cannot fail in the summer months to capture numbers of 

 them. In these situations C. albomaculata, lutea, viridis, and 

 villosa are perhaps the commonest ; while beyond the littoral 

 zone we most frequently meet with pellucida, tuberculata, 

 lutea, etc. The forms here named acerosa and semipunctata 

 seem to be very rare. Their anatomy is not at all known, but 

 their external peculiarities lead to the belief that they may 

 constitute the types of new genera. 



Limnocttheke, nov. gen. — Animal like Cythere, except 

 that the upper antenna? (Fig. 7) are armed with short setas 

 instead of spines. They are five-jointed, slender, the ante- 

 penultimate joint excessively short, terminal joint much elon- 

 gated. Shell rather thin, irregularly tuberculate or spinous. 

 Inhabits fresh water. 



L. inopinata (Baird) ; monstrijica (Norman) . — I have not yet 

 been able completely to examine the structure of these animals, 

 but the conformation of the upper antenna? seems at once to 

 separate them from the foregoing genus. They are very 

 minute, and from their mode of life on clayey bottoms or 

 amongst mud, are not easy of detection. Though hitherto 

 noticed in but few localities, they are probably more common 

 than that circumstance might lead one to suppose. 



