PYCNOGONI DA-CALM AN. 
7 
results when the Pycnogonida are compared with one another. Of all Pycnogonida 
hardly any can be less “ vagile,” as adults or as larva;, than the species of Pycnogonum ; 
yet not only P. gaini mentioned above, but also the common P. littorale of our own 
coasts, show that the species may combine a very wide geographical range with a great 
constancy of specific characters. 
VI.-THE SIGNIFICANCE OF THE DECAPODOUS 
PYCNOGONS. 
Although the present collection contains no species that throws new light on the 
major problems connected with the morphology and phylogeny of the Pycnogonida, 
it may not be out of place here to make a few observations on points raised in 
Prof. Bouvier’s Report on the Pycnogonida of the “ Pourquoi Pas ? ” 
Prof. Bouvier pays the compliment of serious criticism to a little essay (1909), 
in which 1 supported the view (first put forward by Prof. Cf. H. Carpenter) that the 
decapodous condition among Pycnogons is not a primitive survival but a recent 
specialisation. The argument on which I chiefly relied was based on the fact that 
Decolopoda and Pent am/mpi ton, the only decapodous genera then known, are by no 
means nearly related to one another, but exhibit the closest affinity respectively with 
Colossendeis and Ngmphon, two of the normal octopodous genera. This argument 
was greatly strengthened, as I have elsewhere pointed out (1910), by Prof. Bouvier’s 
discovery of Pentapycnon , a decapodous genus widely removed from the other two, 
but approximating very closely indeed to Pycnogonum,; and, while Decolopoda and 
Pent any nip lion can, without much difficulty, be admitted as reasonably primitive forms, 
Pycnogonum and, with it, Pentapycnon, can only be regarded as among the most 
highly specialised of existing Pycnogons. On the other hand, the support which my 
contention seemed to draw from the fact that all three decapodous genera occurred only 
within a restricted geographical area has been quite destroyed by Prof. Bouvier’s later 
discovery of a species of Pentapycnon on the coast of French Guiana—one of the last 
places in the world where one would look for a fauna with antarctic affinities. 
Prof. Bouvier’s argument for the primitive nature of the decapodous forms 
depends, in the first place, on the admitted fact that Decolopoda is, in one respect 
(apart from the number of somites), less specialised than its relative Colossendeis; 
it retains, in the adult state, the chelophores with a Inarticulate scape that are present 
only in the young stages in the last-named genus. Now it may be conceded that, if 
Decolopoda stood alone, it might be “simpler and perfectly logical ” to suppose that 
Colossendeis had been derived from it by the loss of two primitive characters, the 
chelophores and the posterior pair of legs ; but when we have to extend a similar 
supposition to Pentanyniphon and, still more, to Pentapycnon, the argument, though 
