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



VI. Station 373, Lat. 15° 59' 10" N., Ivong. 93° 39' 45'' E., Bay of Bengal, off Pegu 

 coast of Burma, in 195 fathoms. One mature female measuring 202 by 93 

 mm., with brood-pouch and twenty-six eggs. 



These records show that Bathynomus is not uncommon in Indian seas, that it is 

 widely distributed on both sides of the peninsula, but seems to be specially common 

 in that part of the Arabian sea which lies between the Laccadive islands and the west 

 coast of India and is spoken of as the Laccadive sea. 



They show, further, that sexually mature individuals are uncommon in com- 

 parison with immature forms, some of the immature being nearly as large as the 

 mature. The mature male is larger than the mature female. 



v.— OBSERVATIONS ON THE NATURAL HISTORY OF BATHYNOMUS. 



Most of the specimens obtained by the " Investigator " have shown a certain 

 amount of life when taken out of the trawl, but they are not usually active. The 

 mature female, however, which was taken from the comparatively small depth of 194 

 fathoms, was, owing to this reason perhaps, much more active and strongly resisted 

 our attempts to view the contents of its brood-pouch. It lived in a tub of sea water 

 for about two hours, during which time it continued to perform, at regular intervals, a 

 sweeping movement of all its pleopods. When this movement was not taking place 

 the pleopods were held closely applied to the under side of the abdomen ; after 

 intervals which varied betwen 7 and 10 seconds, all these appendages were quickly 

 swept downwards and forwards, and as quickly returned to their former position. 

 This movement is obviously to produce aeration of the blood in the peculiar branchial 

 tufts. One may suppose from the fact that this movement was continued under such 

 abnormal conditions that it was an involuntary one, akin to the movement of a 

 scapognathite of a prawn, which, as is well known, will continue to move long after the 

 animal has been removed from the water. 



Of the five Indian specimens of Bathynomus examined all have carried a small 

 barnacle attached to their pleopods. Two species appear to occur in this position, 

 one of which, described recently by Annandale (25) as Dichelaspis hathynomi, has 

 never been found apart from these large Isopods, while the other, which may be a 

 variety of Dichelaspis occlusa, has also been found on the shallow-water Crustacea 

 Thenus orientalis. 



On plate xii is a photograph of the living specimen ; the hinder part of the body 

 is somewhat raised to allow the sweeping movement of the pleopods. The first 

 pleopod of the right side was damaged and hung down. 



My thanks are due to Dr. J. H. Ashworth of the University of Edinburgh for 

 kindly supervising the reproduction of plates ix — xi of this Memoir. 



