6 
THE VOYAGE OF H.M.S. CHALLENGER. 
become divergently modified, or that two adults might diverge from each other while 
the larvae remain alike, yet we should expect a natural or phylogenetic classification of 
the larvae to stand in some definite and recognisable relation to the natural classification 
of the adults. 
My attempt to discover a relation of this sort at once brought me face to face with a 
serious difficulty. In most of the published descriptions little attention is given to any 
points which are not regarded as diagnostic, and the resemblances, which are of even 
greater scientific interest than the differences, are often completely neglected ; and 
careful study of the published figures soon showed that they are untrustworthy so far as 
relates to points which did not seem significant to the writers. Brevity and exactness of 
diagnosis is of course desirable and essential to the ready identification of species, but 
the description and identification of species is only a means for a more important end, 
the ultimate discovery of the laws of life, and it is therefore desirable that every specific 
description should consist of two parts, a brief diagnosis for purposes of identification, 
and a complete description, or brief monograph, giving all the characteristics ; the points 
of resemblance to allied forms, as well as the distinctive peculiarities. 
The absence of this information renders the establishment of phylogenetic relation- 
ships very difficult, and I soon found that the characteristics which are most significant 
and of most scientific importance are by no means the ones which have been selected for 
diagnosis. The analytical key which Miers 1 gives is probably the best which could be 
devised for ease of identification, and it expresses the general relationship between the 
genera with sufficient accuracy for the purposes of the systematist ; but while most of the 
genera which are usually recognised are natural ones, the points which are of the greatest 
value in tracing the relation between the larvae and the adults are entirely ignored in 
most of the published diagnoses. 
While there can be no doubt that the many differences between the Stomatopoda and 
the other Malacostraca are of ordinal importance, all the species are included in a single 
family, the Squill idae, and the differences between the genera are slight. Excluding the 
genus Leptosquilla, Miers, which is very slightly known, and not represented in the 
Challenger collection, six genera are usually recognised, Squilla, Chloridella, Lysiosquilla, 
Coronis, Pseudosquilla, and Gonodactylus. 
The study of the Challenger specimens shows the necessity for redistributing the 
species which have been associated under the generic name Gonodactylus, and the 
establishment in its place of three genera, Gonodactylus ( sensu stricto), Protosquilla 
n. gen., and Coronida n. gen., and also that it is impossible to draw any natural line 
between Coronis and Lysiosquilla, or between Chloridella and Squilla, and I therefore 
recognise seven genera, Protosquilla, Gonodactylus, Pseudosquilla, Coronida, Lysio- 
squilla (including Coronis ), and Squilla (including Chloridella). My comparison of the 
1 On the SquillidsR, Ann, and Mag. Nat. Hist., ser. 5, vol. v. p. 2, 1880. 
