96 Memoirs of the Indian Museum. [Vol I, 



of depth of the species. In Arcturus, a deep-sea form, it is large, in Cymothoa, a shallow- 

 water genus, it is very small, while in Bathynomus, essentially a deep-sea genus, it is 

 probably absent altogether. 



The broad homogeneous layer between the corneagen and the ends of the vitrellse 

 was plainly seen in all vertical sections, and is shown in the photograph (fig. 4). It 

 seems to be peculiar to the genus Bathynomus. The corneagen seems to have secreted 

 corneal material on its inner side to a certain extent, as well as on its outer side. 



Other Sense Organs. 



Hansen (23) has described from an Indian specimen in the Copenhagen Museum a 

 small sense organ situated in the mid dorsal line of the cephalon close to its posterior 

 border. 



All specimens available in this Museum show the same organ as figured by that 

 author. 



II.— THE MATURE SEXUAL FORMS. 



A mature female specimen was obtained from a depth of 195 fathoms in the Bay 

 of Bengal (pi. ix). This measures 202 mm. in length and 93 mm. in breadth. It 

 possesses a large brood-pouch containing twenty-six undeveloped eggs. The brood- 

 pouch is composed of five pairs of oöstegites attached to the bases of the first five pairs 

 of thoracic legs. Those on the third and fourth legs are the largest, measuring as 

 much as 7 cm. in length and 4 cm. in breadth. Each oöstegite is composed of thin 

 parchment-like material ; with the exception of the last pair they all possess two 

 longitudinal parallel ridges, each oöstegite having the appearance of a leaf with two 

 midribs. At right angles to these ridges, between them and the margin, is a finer 

 venation. The first pair of oöstegites are peculiar. On the upper surface of each is 

 a very prominent ridge, which fits into the groove separating the maxilliped from the 

 thorax, so that the part of the leaf placed in front of the ridge is closely applied to 

 the under side of the head, while the part behind the ridge belongs to the brood-pouch 

 and closes that cavity in front. Furthermore, from the inner end of this prominent 

 ridge is a curved appendage measuring about 7 mm. in length, which in the un- 

 disturbed condition, touches its fellow of the opposite side (text-fig. 5). During life 

 these appendages probably interlock and keep closed the front part of the brood-pouch. 

 The fifth pair of oöstegites are considerably smaller than the others, each possesses 

 one inconspicuous mid-rib : to the inner side of their points of attachment are the 

 generative apertures, semilunar in shape and measuring 7 mm. in length (pi. x, fig. 6). 



The maxilliped of the mature female differs in two respects from that of the im- 

 mature form (text-figs. 6 and 7). Attached to the outer border of the basal joint of this 

 appendage there is, in the mature female, a thin plate measuring 11 by 7 mm. This 

 plate, which is in the position of an epipodite, resembles an oöstegite in its crinkled 

 parchment-like appearance: it differs from those structures, however, in having a hairy 

 margin. As it is only found in the mature oöstegite-bearing female, it may be re- 

 garded as having been produced in co-ordination with the oöstegites. Its occurrence 

 lends support to the view that those structures have been derived from epipodites. 



