154 Dr. J. D. Macdonald on the [Feb. 5, 



February 5, 1874. 

 JOSEPH DALTON HOOKER, C.B., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : 



I. " On the Anatomy and Habits of the genus Phronima (Latr.)." 

 By JOHN DENTS MACDONALD, M.D., F.R.S., Staff Surgeon 

 R.N., Assistant Professor of Naval Hygiene, Netley Medical 

 School. Received January 15, 1874. 



Of all groups of Crustacea the Amphipoda would appear to exhibit 

 the widest range, in the modification of their parts or organs, without 

 obliterating the delicate lines of natural affinity running through them 

 as a whole. This is well exemplified in the interesting paper of Dr. E. 

 Willemoes-Suhm, Naturalist to the * Challenger ' Exploring-Expedition, 

 " On a new Genus of Amphipod Crustaceans" founded by him, and named 

 Thaumops (Phil. Trans, vol. clxiii. p. 629). This genus, although exhibiting 

 many characters in common with Phronima, presents some striking points of 

 difference traceable in the external jaw-feet, caudal appendages, the posi- 

 tion of the generative pore, and certain particulars in its internal anatomy. 



Of the several characters given of Thaumops the presence of only four 

 caudal appendages is perhaps the most exceptional ; for in the generality 

 of the UBOPTERA there are six besides the telson, which is obviously the 

 equivalent of the seventh abdominal segment of Macrura. Thus the six 

 pairs of abdominal appendages, including the tail-fins of the prawn or 

 shrimp, for example, are represented in Phronima and its allies, with the 

 exception of Thaumops. The manner in wlu'ch the fourth and fifth pair 

 of swimmerets and the caudal fins of Macrura are modified in the 

 UROPTERA is well seen in the accompanying figures ; fig. 2 in Phronima 

 and fig. 3 in a neighbouring group of Hyperians, which also serve to 

 show why, at least in the former genus, only five segments have hitherto 

 been recognized in the abdomen. 



During the exploratory voyage of H.M.S. ' Herald,' in the S.W. 

 Pacific, numerous species which I have always been in the habit of 

 referring to the genus Phronima, were taken in the towing-net ; and I 

 may remark that the assumed parasitic habit of these creatures was 

 never, at least, a prominent fact to me ; they were so often taken either 

 perfectly free, or tenanting a nidamental case, such as that subsequently 

 to be described. Those who, like Dr. Suhm, are acquainted with deep- 

 sea dredging are usually cautious how they refer the doubtful products 

 to their proper habitat ; whether it be the bottom that has been reached, 

 or some zone of the watery space above. Indeed it is quite possible for 



