AND THE SUEFACE-riLM OE WATEK. 11 



terior margin, just below the median line. It is quite clear, from 

 the arrangement described, that in spite of the approach of a 

 part of the coloration to the dorsal surface anteriorly, the bulk 

 of it is, as in Sca^pholeberis, markedly within the ventral half of 

 the shell. I have not noticed an actual staining of the chitin in 

 this case, but the colour-patches are due to an enormous number 

 of minute dark brown granules closely packed within the cells 

 lying just under the shell, and the hexagonal shape of these cells 

 accounts for the zigzag edge of the darkened areas. 



The second point to be detailed in relation to this animal, 

 namely, the flattened ventral margin, is very peculiar and deserves 

 careful attention. Examined from the side nothing can be seen 

 but a perfectly straight edge giving rise to a few slender setae, 

 but looked at from below it becomes evident at once that this 

 ventral portion of the shell is very much specialised (PI. II. fig. 4). 

 The main features, as seen when the valves are closed, are thus 

 well described by Prof. G. iS. Brady, F.R.S., in his "Mono- 

 graph of the Eecent British Ostracoda " * : — " The ventral surface 

 is bounded by two conspicuous elevated arcuate ridges, one on 

 each valve, which together enclose a flattened lozeuge-shaped 

 area. Parallel to the contact-margin of each valve runs another 

 straight but much less conspicuous ridge, which, towards the 

 front, curves outward and joins the external ridge at an acute 

 angle, the union of the two forming a slight elevation, from 

 which a single ridge runs forward, gradually merging in tue 

 flattened encircling flange of the anterior border." Tiiis account 

 is given in conuection with the male, but the arrangement is the 

 same in both sexes, the only difierence being that the modified 

 area is comparatively larger in the female than in the male. 

 In addition to the two chitinous ridges, there are also, on the 

 ventral portion of each valve, some lines of simple setae. By 

 far the longest of these is the one running quite close to and 

 parallel with the inner ridge on its outer side. The others are 

 found in the somewhat semicircular depression formed by the 

 bending of the inner to join the outer ridge, which depression, 

 by the way, is most strikingly similar, both in position and shape, 

 to that found on the anterior part of the shell- valves of Bcapho- 

 leheris. 



The habits of Notodromas are almost identical with those of 



* Transactions of the Linnean Society, vol. xxvi. 1868. 



