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



part of foot-jaws as in the higher Crustacea. The five succeeding pairs 

 are more especially restricted to the thorax, the third or middle one being 

 stoutly chelate, normally directed backwards, with the pollex superior, and 

 enjoying a very considerable range of motion. 



The first pair is usually thrown forwards over the head, and the last 

 backwards over the abdomen, the first flexure corresponding with the 

 first swimmeret ; the second pair is the longest. 



The fourth, fifth, and sixth thoracic segments are each furnished with 

 a pair of elongated and laterally compressed respiratory vesicles, connected 

 with the posterior and inferior part of the epimeral pieces behind the 

 articulation of the corresponding limbs. These vesicles increase in size 

 from before backwards ; and indeed a very rudimentary one may be seen 

 behind the third pair of limbs. The last, or seventh, thoracic segment is 

 of unusual length, tapering posteriorly, to correspond with the narrowness 

 of the abdomen, in which also the segments are of greater length than 

 those of the thorax. It has been already stated that in Phronima, as in 

 the Macrura, there are seven segments in the posterior division of the 

 body ; functionally, however, three of these may be said to belong to the 

 abdomen and four to the tail. The three abdominal segments bear each 

 a pair of swimmerets, arising near their posterior border, and consisting 

 of a stout or inflated foot-stalk and two narrow, acuminate, annulated 

 and setaceous terminal pieces. 



The three anterior of the four caudal segments bear a narrow^ fan, con- 

 sisting of three pairs of slender appendages furnished with two short 

 styliform tips. The first and third of these caudal members are much 

 longer than the second. 



The oral organs (with the exception of the jaw-feet), the large chelae, 

 and the foot-stalks of the swimmerets are tinted with a rich purple pig- 

 ment. All the other parts are hyaline and transparent. 



EXPLANATION OF THE PLATE. 



Pig. 1. Lateral view of Phronima (species ?). With the exception of the antennae, 



the limbs and appendages of one side only are represented, magnified about 

 9 times. 



Fig. 2. The abdomen and tail of the same, further enlarged, to show the several seg- 

 ments, numbered (from before backwards) 1, 2, and 3, with swimmerets, and 

 4. 5, and 6 bearing caudal appendages, while 7 is the terminal segment or 

 " telson." 



Fig. 3. The abdomen and tail of a Hyperian for comparison, all the numbers having 

 the same signification *. 



The evidence of Dr. Willemoes-Suhm supports my own experience, that 

 there is no metamorphosis in this group ; and as it is very probable that 

 the history of the development of Thaumops would resemble that of 

 Phronima, the following observations may be of some importance, as 



* l r , 2', 3', 4', 5', and 6' being the appendages of the corresponding segments. 



