Only one genus of this family is recognized by M. Milne-Edwards 

 in his work on the Crustacea, though Dr. Leach had many years 

 ago established a second ; the character upon which that genus was 

 founded by Leach is not considered by M. Edwards as of generic 

 importance ; but having observed another character equally remark- 

 able, which occurs in all the known species of the group which that 

 genus represents, I consider Leach's genus ought to be adopted, and 

 I now propose giving the characters of the two genera at greater 

 length than they have yet been done. 



Genus A pus, Scopoli. 



Clypeus corneo-coriaceus. Corpus molle, cylindricum, Seg- 

 mentum caudate lamina producta non instnictu7n. Pedum 

 primi paris appendices, aut rami, longissimi, Jlexibiles. 



In the genus Apus, the tail-segment of the body is rounded, and 

 has no plate or prolongated appendage between the two long setae 

 or filaments. The first pair of feet are very long, dividing into three 

 cylindrical branches, the external one of which is very long, in some 

 species equalling in length the whole body with the tail filaments in- 

 cluded : they are very flexible, possess much motion, and are very 

 conspicuous. These organs at once distinguish the genus, and they 

 possess the same general character in all the species hitherto known. 

 Four species have only as yet been described, and I now propose to 

 add to that number a fifth. 



1. Apus cancriformis, Schseffer. Clypeo corporis plusquam 

 dimidiam partem tegente, ovato, olivaceo, corneo ; ramo externo 

 pedum primi paris longitudine clypeum aquante. 



Long, toti corporis 2\ poll. ; lat. clypei \\ poll. 



Pro Synonymis vide " Baird's Nat. Hist, of the British Entomos- 

 traca, Ray Society's Publications, 1850." 



Hab. In Europa ; detecta in Anglia, Gallia, Borussa, &c. In Africa 

 Septentrionali ; detecta in Tunisia, collegit Dominus L. Frazer ; in 

 Algeria, collegit M. Lucas. Museum Britannicum. 



The colour of this species is brownish yellow or olive clouded with 

 marks of a deeper hue. The carapace is oval and extends over nearly 

 two-thirds of the body of the animal. The keel which runs down the 

 centre of the caraj)ace is pretty strong, and the deep notch at the po- 

 sterior extremity is lunated in shape and has its edges finely toothed. 

 The external branch of the first pair of feet is about the length of the 

 carapace, while the caudal setae are nearly as long as the whole body, 

 and are covered with numerous short hairs. The abdominal portion 

 of the body not covered by the carapace is studded all over with cir- 

 cular rows of stout hooked spines of a dark brown colour. 



2. Apus Guiluingii, Thompson. Clypeo corporis vix dimi- 

 diam partem tegente, quadrato, membranaceo, nigrescente ; 

 ramo externo pedum primi paris longissimo, totum corpus, jila- 

 mentis caudalibus inclusis, excedente. 



Apus Guildingi, Thompson, Zoological Researches, Fasc. v. 108. 

 t. G. f. 3 ; M. Edwards's Hist. Nat. Crust, iii. 561. 



