300 



found themselves in a difficult situatiml, qince in the species to which 

 the given specimen could have been related, the "male" had already 

 been described. We are convinced that neither the length of antennae 

 nor the degree of fusion of the first pereon, somites can serve as good 

 246 diagnostic characters. The number of ventral, marginal, and mandibular 

 denticles also varies within a known range and per se is less suitable for 

 diagnosis. However, the combination of these characters can serve as a 

 basis for the identification of species. Practically, from a size of 30 mm, 

 the sex of the crustacean can be identified because the development of 

 oostegites commences now in the female. The absence or presence of 

 lateral denticles on the mandible is obviously a stable character although 

 their number (when present) is liable to variation. An increase in number 

 of marginal denticles to 17-18 is also an important character, although 

 variations within the range of 12-16 denticles hardly qualifies it as such. 

 The length ratio of the rami of the uropods can be used as a species 

 character only in combination with other characters. The absence of an 

 arcuate row of denticles among the ventral ones may also be used in 

 identification, as a character independent of sex and age. Here, too, the 

 morphology of the "egg forceps" appears quite promising as a structure 

 associated with reproduction and, therefore, a more reliably genetically 

 fixed character; unfortunately, it is inherent only in mature females. 



KEY TO SPECIES OF GENUS CYSTISOMA 



1. Mandibles with one central denticle; lateral denticles absent ..... 3. 



— Mandibles with one central and one-two lateral denticles 2. 



2. Pereopods thin, particularly pair V; 2nd segment of pereopods VII 

 weakly broadened proximally 4. C. longipes (Bov.) 



— Pereopods with broadened segments, particularly VI-VII; 2nd seg- 

 ment of pereopods VII pyriform, proximal width four times distal 

 width 5. C. latipes (Steph.) 



3. Only two pairs of ventral denticles — anterior and glandular; denticles 

 of arcuate rows not developed 3. C. fabricii Stebb. 



— Four-six pairs of ventral denticles; denticles present in arcuate 

 rows 4. 



4. Adult females with highly developed glands in distal part of 6th 

 segment of pereopods III-VII and also with apical glands on anten- 

 nae I and exopodites of uropods; exopodites distinctly longer than 



endopodites; urosome with uropods longer than pleon 



I.e. pellucida (W.-Suhm) 



— Adult females without distinct glandular inclusions on antennae and 

 extremities. Rami of uropods equal in length; urosome with uropods 

 not longer than pleon 2. C. magna (Wolt.) 



