I. On the anatomy and habits of the genus phronima (Latr.)

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. R. Willemöes-Suhm, Naturalist to the ‘Challenger’ Exploring-Expedition, “On a new Grenus of Amphipod Crustaceans” founded by him, and namedThaumops (Phil. Trans, vol. clxiii. p. 629). This genus, although exhibiting many characters in common withPhronima , presents some striking points of difference traceable in the external jaw-feet, caudal appendages, the position of the generative pore, and certain particulars in its internal anatomy. Of the several characters given of theThaumops the presence of only four caudal appendages is perhaps the most exceptional; for in the generality of the Uroptera 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 inPhronima and its allies, with the exception ofThaumops . The manner in which 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 inPhronima 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.