98 Memoirs of the Indian Museum. [Vol.. I, 



segment two pairs of tongue-shaped plates of hard chitin, easily distinguishable from 

 the soft leathery cuticle of the lower surface of the thorax. These plates articulate 

 externally with the base of the movable epimera. The members of each pair are 

 separated by a narrow V-shaped area of soft cuticle ; while they are both separated 

 from the corresponding pair of the opposite side by the median area of soft cuticle 

 about 2 cms. in breadth. 



In the gravid female the ventral surface of the thorax is deeply concave ; thereby 

 the capacity of the marsupium is increased. On examining this surface, tongue- 

 shaped plates similar to those found in the other forms are seen, but where these are 

 in contact with the epimera the pairs are themselves united. From their union a thin 

 band of hard skeletal material arises, which is continuous across the mid ventral line 

 with its fellow of the opposite side. Thus in the mature female alone there are com- 

 plete skeletal sternites in the thoracic region. These sternites are very conspicuous 

 owing to their white colour and hard consistency. In the mid ventral line they each 

 form a V-shaped figure (pi. x, fig. 6). They are present from the second to the sixth 



segment. 



The Eggs. 



The eggs of Bathynomus are large spheres of a pale yellow colour, measuring as 

 much as II mm. in diameter. This is probably the largest recorded crustacean egg. 

 The brood-pouch, which contained twenty-six of these eggs, also contained eight empty 

 egg-shells probably from a former brood. The eggs seemed to be quite undeveloped, 

 being entirely made up of liquid yolk material enclosed in a thick parchment-like shell. 



The Mature Maj.e. 



A mature male form measuring 270 mm. by 118 mm. was obtained off Ceylon. 

 This, although the largest recorded individual of the species, is not much larger than 

 the American specimen, but it differs from that in being provided with copulatory 

 stylets in the usual position attached to the endopodites of the 2nd pleopods. This 

 appendage does not differ, except in minor details, from that of B. döderleini, already 

 portrayed by Bouvier. 



III.— ON CERTAIN DIFFERENCES BETWEEN THE INDIAN AND 

 AMERICAN FORMS OF BATHYNOMUS GIGANTEUS. 



Figure 4 (pi. x) was drawn by Babu Mondul, draughtsman to the Marine Survey. 

 The work of this artist is usually so accurate, that I was surprised to find his 

 rendering of the basal plates differed somewhat from Bouvier' s figure of the same 

 structures. In order to be quite clear on this point, I excised the membranous attach- 

 ment of one of the pleopods and after clearing with caustic potash, drew it en- 

 larged, with the camera lucida. As can be seen from the resulting figure 3, there 

 are five separate plates in this situation, four on the anterior side and one on the pos- 

 terior; whereas Bouvier' s figure shows only two plates on the anterior side. Subse- 

 quent examination of all available specimens showed that five separate plates were 



