PHRON1MA SEDENTARIA. 25 



short, terminating in a minute double point, and flanked on 

 each side at the base with two little wing-like appendages. 

 These are smooth and arcuated upon the upper margin, 

 but straight and regularly pectinated along the lower. 

 The next two pairs of legs are long and simple ; the 

 succeeding pair are developed into the form of a perfect 

 claw, each branch having a tubercle near the base on 

 the inner edge, these tubercles being finely tuberculated ; 

 the last two pairs of legs are short and simple. The 

 natatory appendages are short, but have a robust peduncle. 

 The caudal appendages resemble each other, but the 

 penultimate pair are about half the length of the 

 others. They consist of a long, slender peduncle and a 

 couple of styliform branches. The middle tail-piece is 

 very small. 



Dr. Pagenstecher, of Heidelberg, has published a very 

 interesting anatomical and physiological memoir on this 

 species in Wiegmann's " Archiv fiir Naturgeschichte," 

 for 1861, in which he has made us acquainted with the 

 early and intermediate states of the animal. In the 

 earliest condition the antennae are very small, dilated, and 

 jointlessj the seven pairs of legs are of uniform size 

 and shape, each consisting of seven joints, including the 

 small basal joint by which it is attached to the body, and 

 the very minute terminal hook. The joints of the tail 

 are almost undeveloped, the whole tail being scarcely 

 larger than the preceding segment. In the intermediate 

 state the third and fourth pairs of legs are considerably 

 elongated, and the fifth pair have become cheliferous.* 

 The tail and its appendages have also acquired consi- 



* The progress of development in this genus offers a curious contrast to 

 that of Bmchyscclus crusculum as described by Spence Bate, "Annals of 

 Natural History " for July, 1861, in which the sixth pair of legs are cheliferous 

 in the young stage, becoming simple in the adult. 



