3 I 



[No- 7. 



by Mr. Brady from Ceylon under the name of I. Haleyi. On 

 closer examination I find however so much that differs from the 

 description and figures given by that author, that at present I 

 do not feel warranted in identifying both, especially as the se- 

 veral species of this genus are so nearly related as to need a 

 much more detailed examination for their identification than 

 that by the above mentioned author. In some respects it re- 

 sembles rather the European species, I. agilis Kurz, but the ca- 

 rapace of the latter species is much more dilated and differs too 

 in the total want of lines of growth, owing to the complete 

 exuvation of the shell in that species. 



Description. — The length of old female specimens almost 

 reaches lV2mm, and this form attains accordingly a somewhat 

 larger size than do the three European species : I. sordidus (Lie- 

 vin), agilis Kurz, and acutifrons G. 0. Sars. 



The form of the carapace varies a little with age. In very 

 young specimens it exhibits, as seen laterally, a somewhat re- 

 gular triangled form, successively widening from before to be- 

 hind, and is more abruptly truncate posteriorly. In old female 

 specimens (PI. 4, fig. 1), however, from the considerable dila- 

 tation of its upper part, limiting the incubatory cavity, and the 

 successive growth of the valves, it assumes a more oblique form, 

 the anterior part of the dorsal face being considerably vaulted, 

 almost gibbous, and the posterior edges very oblique. In all speci- 

 mens, the dorsal edge of the carapace terminates posteriorly with 

 an obtuse angle, located considerably above the longitudinal axis of 

 the shell, whereas the inferior and posterior edges of the valves 

 pass into each other by an even, though rather prominent curve. 

 The relation between the height and the length of the carapace 

 is well-nigh the same, or the length very little greater. The 

 head is comparatively very small and, viewed laterally, of trian- 

 gular form, terminating in front with an acute angle; its inferior 

 edge runs posteriorly, being nearly straight, with only a slight 

 rounded prominence just behind the middle, indicating the place 

 where the antennulae are affixed. In young specimens, the head 

 extends nearly in the longitudinal axis of the shell, whereas in 



