324 GeofFrey Smith 



any raarked break: tliis group includes the genera Leptochelia, 

 Heteì'otanais, Paratanais aud tben the blind genera Leptognathia, 

 Taiiaopsis, and Typhlotanais. Tbis group is beld togetber by the 

 possession of a comb on the chela (PI. 20. Figs. 7, 21 etc.), by the form 

 of the antennae in the male, and the abseuce of any other marked 

 dilferences which split off certain of the other genera. The most 

 perfect series from our point of view goes throiigh the species of 

 Leptochelia to Paratanais, Heterotatiais standing apart through quali- 

 tative variations; aud the passage from Paratanais to the blind 

 genera, thoiigh I think certain, is not very immediate. Our method 

 is first to describe the kind of high and low dimorphism that 

 exists within tbe limits of a large species and then see if our series 

 of allied species fits into any scheme with relation to it. The species 

 chosen is Leptochelia dubia. There has been much diftìculty with 

 regard to the limits of tbis species and this is reasonably cleared 

 up in the Appendix. The Variation in size of 74 definitively adult 

 males is given in Table 2; it extends from 2 — 4 mm.; and in the 

 degree of development of the chela, as measured by the length of 

 the forceps, it exhibits the phenoraenon of high and low dimorphism 

 very markedly. Figures drawn to scale of chelae of high and low 

 males are given (Figs. 7, S and 9). The antennae of the male is 

 long and has from 9—11 joints (Figs. 3 and 4). It must be noticed 

 that low males have often longer and more numerous sensory hairs 

 than high males (Figs. 3, 4, 5 and 6). (The relation of these high 

 and low males to Feitz Müller's males is discussed in the Appendix). 

 All the males bave the mouth parts degenerate : up to the last moult 

 they bave the form shown in Figure 10. The adult ovifcrous fomales 

 bave the form shown in Figures 11 — 13; they measure about 3 mm. 

 The chela is very differeut to that of the male, being much smallar 

 and lacking the tubercles on the lower limb. The antenna also is 

 quite different, being 3-jointed and destitute of sensory hairs. The 

 uropod of the adults of both sexes has a 6-jointed endopod aud a 

 one-jointed exopod. During the larvai stages the endopod steadily 

 increases in size proportionately to the exopod, as shown in the 

 series Figs. 14 — 17. \Ye must now look for a moment more uarrowly 

 at the chela of the male. In Fig. 7 which depicts the chela of a 

 high male it should be noted that the two serrated tubercles ou the 

 lower arm of the forceps are far apart, but much more nearly ap- 

 liroximated in the low male Fig. 8, while in Fig. 9 the two tubercles 

 are running together with a continuous line of serration between 



