10 
THE VOYAGE OF H.M.S. CHALLENGER. 
This ancestral form must have been very similar to two closely related living species, 
Squilla bradyi, Milne-Edwards, and Gonodactylus trachurus, Miers, which are referred 
by Miers to the genus Gonodactylus on account of the enlargement of the base of the 
dactyle, and to Squilla by Milne-Edwards on account of the presence on the same 
organ of marginal spines, and the flatness of the hind body. Their points of 
resemblance to Gonodactylus are also points of resemblance to Protosquilla, and as they 
differ from all the species of Gonodactylus in the flatness of the hind body, and the 
presence of spines on the dactyle, there can be no doubt of the propriety of placing 
them in a distinct genus, for which I propose the name Coronida. Coronida has, like 
the convergent species of Lysiosquilla and Squilla, small eyes, antennary scales and 
uropods, a flat hind body, an armed dactyle, and a wide rounded telson, and there can 
therefore be no doubt of its close relationship to the ancestral type of these genera. 
The species of Coronida, Pseudosquilla and Gonodactylus, are closely related, but not 
in such a way as to indicate that any one genus is the ancestor of the others. The two 
latter resemble each other, and differ from the first, in the fact that the hind body is 
convex and narrow and bent downwards at the tip, while it is straight and flat and wide 
in Coronida. 
Gonodactylus and Coronida resemble each other and differ from Pseudosquilla in the 
presence of an enlargement at the base of the dactyle of the raptorial claw, while 
Pseudosquilla and Coronida resemble each other and differ from Gonodactylus in the 
presence of marginal spines on the dactyle. 
This triangular relationship can be accounted for only on the hypothesis that they are 
the divergent descendants of an ancestral form which each one of them resembles in 
certain features, to which, in each genus, secondary differences have been added. 
As there is no reason to suppose that this divergence is recent, we should not expect 
to find this ancestral form still represented by living species, but as the living species of 
Protosquilla exhibit, like this hypothetical stem form, features of resemblance to each of 
these genera, it is not only probable, but almost certain, that they are much more directly 
descended from the ancestral form than any of the species of Gonodactylus or Pseudo, 
squilla or Coronida ; and, of course, than any of the Lysiosquillse or Squillse. 
Protosquilla resembles Gonodactylus in the small size and flatness of its carapace, in 
the presence of an acute spine on the rostrum, in the unarmed dactyle dilated at its base, 
in the height of the narrow hind body, the terminal somites of which are bent down- 
wards, and also in the small size of most of the species. 
It also resembles Pseudosquilla in most of these features, but the dactyle of 
Pseudosquilla is without the basal enlargement, and is usually armed, like that of Coronida 
and the Squillse and Lysiosquillse. 
Coronida resembles Protosquilla in the small size of its eyes, antennary scales and 
uropods, the flatness of the small carapace, the enlargement of the base of the dactyle, 
