42 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 120 
among the morphologically similar but allopatric species, jollae and 
kolpos. 
We can only speculate as to the mechanics of a key-lock mechanism 
for inhibiting hybrid mating in the jollae group. The existence of 
such a mechanism at this time rests on the absence of hybrids and 
the fact that no Labidocera adult female of any species has been seen 
bearing the spermatophore of another species. In general, copulation 
in crustaceans occurs soon after the female moults and before the 
cuticle has hardened. If this is true in pontellids, the possibility 
of damage makes it unlikely that female secondary sexual characters 
are subjected to great pressure during clasping or when used as sites 
for leverage. As noted earlier, the jollae male has been observed 
holding the female about the urosome with its chela. To avoid 
injury to the recently moulted female and to permit whatever maneu- 
verability is needed for manipulating and cementing the sperma- 
tophore, the chela could serve as a ring loosely encircling the female 
urosome. The urosome in turn should have the means to prevent 
both interference with prosome-urosome articulation and separation 
of the mating pair, i.e., suitably placed anterior and posterior me- 
chanical stops. 
In the jollae group the female genital segment anteriorly bears 
one or more conspicuous swellings and posteriorly it expands gradually 
in circumference somewhat like a plug. In diandra, a strong shoulder 
abruptly increases the posterior girth of the elongated genital seg- 
ment while in jollae and kolpos the right caudal ramus is greatly 
expanded beyond the lateral limit of the urosome. These otherwise 
peculiar asymmetries appear to fulfill the requirements for mechan- 
ical stops limiting the extent of slippage of an encircling chela. In 
fact, the arrangement in diandra appears to be equally effective for 
both male morphs. 
Evolution of Specific Characters in the jollae Group 
Comparison of the three species described above reveals one out- 
standing feature. Despite predominantly allopatric ranges, morpho- 
logical separation of these species is concentrated in secondary sexual 
characters. On the other hand, no apparent differences were seen in 
either feeding or swimming structures unaffected by sexual maturity; 
that is, the three species show unmistakable evidence of strong selec- 
tion pressure for diversification of copulatory structures but little 
to no modification from basic morphology of other adaptive structures. 
The possibility that copulatory adaptations differentiated as such 
in totally allopatric daughter populations cannot be ruled out at this 
time; however, the likelihood of achieving by chance the orderly 
