8 
THE VOYAGE OF H.M.S. CHALLENGER. 
2. Dactyle of raptorial claw not dilated at the base, but usually armed 
with marginal spines. 
(1) Primary marginal spines of telson small, with no more than 
four secondary spines between the submedian and the inter- 
mediate ; outer spine of basal prolongation of uropod usually 
longer than the inner ; dactyle of raptorial claw with not 
less than six marginal spines. 
Genus Lysiosquilla (PI. X. figs. 8-16). 
(2) Primary marginal spines of telson large, with more than four 
secondary spines between the intermediate and the sub- 
median ; inner spine of basal prolongation of uropod longer 
than outer ; dactyle of raptorial claw usually with no 
more than six marginal spines. 
Genus Squilla (Pis. I., II., III.). 
In each of these genera there are certain characteristic or typical species, which are 
sharply cut off from all other genera, but it is difficult to give any absolutely diagnostic 
generic characteristics, as, in addition to the divergent and typical species, each genus 
also contains a few. species which are more primitive, with the characteristics of the 
genus very slightly developed, and with features of resemblance to the primitive 
species in other genera. 
The form of the dactyle of the raptorial claw affords a ready means for distinguishing 
species, and most of the genera are based upon peculiarities of this organ, which furnishes 
a tolerably satisfactory index of relationship, but gives no clue to the wider and more 
deep-seated affinities; but as soon as we ignore the preponderating importance which has 
been attached to the big claw, and take the whole organisation into consideration, we 
find that there are, in each genus, species which exhibit evidences of relationship to a 
common type or ancestral form, from which the various genera have diverged, and which 
was characterised by the possession of small, sub cylindrical eyes, an acutely pointed 
rostrum, a smooth hind body, a short wide smooth carapace, very small antennary scales 
and uropods, and a telson which was wider than long, with the marginal spines crowded 
backwards, and the posterior border transverse, or nearly so. 
From this primitive form, which is represented at the present day, probably with 
slight secondary modifications, by the various species which I have associated under the 
generic name Protosquilla, the various genera have diverged, and while it is not at all 
probable that any species which we know is the actual stem form of the order, yet there 
is ample evidence to show that this was characterised by the features which the various 
species of Protosquilla have in common, and that it must have been more nearly allied to 
them than to any other species with which we are acquainted. Thus, for instance, the 
