b AMPHll'ODA NORIIAUA. 



the result of the absoii)tion of part of the lower autenuae ^^^thin the 

 head, thus diiving, as it Avei'e, the eyes upwards. 



The upper autenua? arc deficient of the auditory ciha — organs which 

 appear to be peculiarly adapted for the transmission of a vibrating 

 sensation, such as sound, when water instead of air is the medium. 



The lower antcnnte in the male are considerably longer than in 

 the female ; in the former they are often as long as the entire 

 animal, whereas in the latter they reach to about two-thirds. I say 

 often, in reference to the antennae in the male, since the extreme 

 length of the organs appears to be reached only in the older animals. 

 We often meet vrith individuals quite as large, in which the antennae 

 are not so long. 



The exposed portion of the lower antennae consists only of three 

 articulations to the peduncle. The first two, throughout the genus, 

 are absorbed in the head (PI. I. fig. 1 c), and are not visible on a 

 lateral inspection. The olfactory denticle is not present, the organ 

 most i^robably being altered in form, and perhaps character, to meet 

 the peculiar conditions of its existence, since, unlike most other Am- 

 pliipoda, the Tcditri never enter the water. 



The mandibles are veiy powerful, and suppKed -ttdth a large molar 

 tubercle furnished with rows of minute denticles on the surface. The 

 biting extremity in each mandible is supplied with a double row of 

 denticles, both formed upon one type ; the inner row is supported 

 upon a plate that is moveable. Between the apex of the mandible 

 and the molar prominence are a few strong, curved, hairy spines 

 directed towards the oesophagus. 



The mandibles are not famished with an ai-tieulated appendage, 

 which suggests the idea that land species may not require certain 

 parts that are necessary to those which frequent water, whilst those 

 parts which are requii'ed are more perfected in order to fulfil their 

 proper functions. 



The maxillipeds are non-unguiculate — that is, the last articulation 

 is not produced to a point or nail — and furnished with a few bail's. 

 There are short stout teeth upon the apex of the plate or squamiform 

 process of the ischium. 



The whole apparatus formed by these gnathic organs is pro- 

 jected, — a circumstance which enables the animal the easier to gather 

 its food from fixed positions, and in this respect differs fi-om those 

 that feed upon materials suspended in water. It is from this pecu- 

 Har form of the mouth (which in its protinision much I'esembles that 

 of the Locust) that, according to Leach, they derive their specific 

 name of Locusta. 



The first pair of gnathopoda are simple in the genus, and in this 

 species are stronger than the second ; or it would be more correct to 

 observe that the second are weaker than the first, and are generally 

 tucked up beneath the pereion, and are probably seldom used. 



The coxae of the foiu" anterior paii-s of legs are nearly as deep as the 

 pereion. The fifth is scarcely less deep than the fourth, but is con- 

 siderably broader, and divided into two equal plates, an anterior and 

 a posterior, the ischium articulating in the intermediate cleft : the 



