326 Geoffrey Smith 



having 4jomts iu tlie endopod and 2 in the exopod (Fig. 28). This 

 little form iu its size, chelae, antenuae and iiropod forms a beautiful 

 trausition from tlie geuus Leptochclia to Paratanais. P. Batei (PI. 21, 

 Figs. 40 — 43), a typical member of the geuus, is a little smaller than 

 L. mei'gelUnae, aud iu correspoudeuce the characters under couside- 

 vatiou have progressed a little fuvther than in the foregoing. The 

 chela is yct more reduced (Fig. 40), the antennae (Fig. 42) more 

 stumpy and with louger hairs, the uropod has the endopod aud 

 exopod both with 2 joints and practieally assimilated, except that 

 the endopod is a little longer and stouter (Fig. 43). 



We have so got a perfect transition from L. Corsica through dubia, 

 inei'mis, mercantilis, mergellinae, to Paratanais. We have now to 

 pass to the blind genera, LejJtognathia, Tanaopsis^ Typhlotanais (see 

 Sars, Crustacea of Norway, Isopoda). The striking thing about these 

 forms is the great discrepancy in size between the males and females. 

 Thus in T. laticaudata, the male measures 1.4 mm. and the female 

 3.2 mm. and this is also the case with all the species the males 

 of which are known. The male in the form of the chela, the an- 

 tenna and the uropod betrays a distiuct likeness to Paratamiis 

 (Figs. 44 — 46), but it is doubtful how nearly allied they are. These 

 blind forms therefore by no means eontrovert our rule, because the 

 males beloug to a dìstinctly small category and in correspoudeuce 

 we find the chela reduced aud the antenna aud uropod developed 

 in the way which we have found to be characteristic of the smal- 

 ler forms. 



The rather anomalous species iucluded iu the genus Heterotanais 

 (PI. 21, Figs. 29 — 39) dififer qualitatively from the forms considered in 

 several respects, especially in the curious broken form of the chela 

 in the male and the swolleu antennae of the female (Figs. 31 

 and 34). We are here confronted with a qualitative ditìerence which 

 is very hard to deal with aud we shall find this also to a certain 

 extent in the Lamellicornia. 



We may now tabulate our series as follows, passing from large 

 forms with highly differentiated clielae in the raales, with long an- 

 tennae provided with few and short seusory hairs, with an uropod 

 in which the endopod is much longer than the exopod, to smaller 

 and smaller forms in which these characters become progressively 

 altered in a definite way. These forms are: 



