Asellus, appears to be derivable from a structure consisting in principle 

 of a terminal ventral groove associated with which are four terminal ele- 

 ments: a mesial process arising from the medial edge of the ventral 

 groove; a cannula, essentially a tubular prolongation of the ventral 

 groove; a lateral process arising from the lateral edge of the groove; 

 and a terminal caudal process. Loss or modification '^^ these elements, 

 it has been suggested, can produce the conformation unique for each species 

 of Asellus. 



A final pair of abdominal appendages project backwards from the posterior 

 border of the abdomen; these appendages are the uropods. Each (Fig. 7D) 

 consists of a basal segment, the peduncle, and two distal segments or rami, 

 an inner one, the endopod, and an outer one, the exopod. The upper sur- 

 face of the region referred to here as the abdomen in effect constitutes 

 the telson, also referred to as the pleotelson (Fig. 7E) . 



EXAMINATION TECHNIQUE. A stereoscopic and a compound microscope, a pair 

 of fine forceps, a mounted needle, a petri-dish (or similar container) and 

 microscope slides and coverslips are equipment needed for species identifi- 

 cation. Preliminary examination and dissection should be made using the 

 stereoscopic microscope with the specimens immersed in 70-80% ethyl alcohol 

 and illuminated by reflected light against a dark background. Further 

 identification is carried out by removing appropriate appendages or body 

 parts, mounting these on a microscope slide in a small amount of the alco- 

 hol from which they were withdrawn, and examining by transmitted or re- 

 flected light as appropriate. Such preparations are temporary; more per- 

 manent ones may be made using one of several mounting reagents now com- 

 mercially available which do not require passage of specimen material through 

 a series of other reagents. The author uses "Euparol" (George Gurr Ltd., 

 U.K.). Readers are warned, however, that many such mounting reagents also 

 include clearing agents and if their action is too severe distortion and 

 contraction of mounted material (particularly of the endopod tip of the 

 second pleopod of male Asellus specimens) may occur. It is important that 

 this does not happen. Readers are also warned that endopod tips of the 

 second pleopod of male Asellus specimens should be viewed in a variety of 

 positions so that a better appreciation of the arrangement of terminal 

 parts is gained. 



11 



