376 A HISTOBY OF RECENT CRUSTACEA 



CHAPTER XXIV 



TRIBK IV. — ASELLOTA 



The, second pair of antennae are elongate ; the maxillipeds 

 are furnished with an epipod, have the second joint pro- 

 duced into a plate, and the ' palp ' consisting of five dis- 

 tinct joints. The first pleopods in the female are usually 

 transformed into a single opercular plate, and in the 

 male are variously modified ; the four following pairs are 

 branchial; the uropods are terminal, or, if lateral, not 

 remote from the apex of the pleon, one- or two-branched, 

 or consisting of a single joint. There are two families, 

 the Asellidae. and Munnopsidas. 



Family 1. — Asellidce. 



The mandibles have a denticulate cutting edge, a 

 molar tubercle, and usually a three-jointed ' palp.' The 

 limbs of the perseon are prehensile or ambulatory, not 

 specially modified for swimming. The marsupial pouch is 

 formed of plates pertaining to the first four, or to the 

 second, third, and fourth segments of the peraeon. Some 

 twenty-five genera are included in this family, many of 

 them exhibiting very striking peculiarities. 



Asellus, Geoffrey, 1762, shares with Mancasellus a cha- 

 racter exceptional in the tribe to which it has given its 

 name, in that the pleon in both sexes has the first pair of 

 pleopods quite small, consisting in the female of two un- 

 jointed oval plates, while the second pair are opercular, 

 but not fused together in either sex. The female has but 

 four, the male has five pairs of pleopods. The heart ex- 

 tends from the pleon through the perason. This genus 

 belongs exclusively to fresh water. Asellus aqiiaticus 



