338 OX A COLLECTION OF ECHIURIDS, WITH AX ATTEMPT TO 



PART II. 



AN ATTEMPT TO REVISE THE GROUP ECHIUROIDEA. 



In determining the species of the Echiurids collected by Dr Willey during his 

 voyage to the East in 1895 — 97, a considerable difficulty arose owing to the scattered 

 nature of the literature referring to the more recently described species. The number 

 of these species has very much increased since the publication of Greef's Monograph 

 in 1879, and has even doubled since the date of Rietsch's Thesis, 1886 1 , so that little 

 excuse is needed for an attempt to revise the group. In the following pages I have 

 taken Greef's Monograph as a starting point, and must refer to his work for the 

 literature prior to the date of his publication — except for one or two papers there 

 omitted — for the list of synonyms, and for an account of a small number of species 

 which for the most part are too inadequately described to be satisfactorily recognisable. 



THE DETERMINATION OF THE SPECIES. 



In determining the species of an Echiurid, the following facts are of importance : — 



(I.) The size both of the trunk and of the proboscis. Echiurids are extremely 

 extensile, and so the limits of their size vary widely. When killed, as a rule the 

 animal contracts violently, but this is by no means always the case, and I have given 

 on Plate XXXIII. Figs. 5 and 6, the outlines of two specimens of Th. neptuni, both 

 supplied by the Plymouth Laboratory, and both of about the same weight, but one has 

 been killed expanded and the other contracted : it will be seen that the difference in 

 outline is remarkable. 



(II.) The colour. This is only of value when described from the living animal, 

 in which, however, it seems to vary a good deal both in different individuals and in 

 the same individual in different states of contraction. Echiurids are often very bril- 

 liantly coloured, the bright green Bonellias and Thalassemias and the deep red 

 ThaUasemas, with their violet stripes and white spots, form very striking objects until 

 they are put in spirit, when the colour rapidly fades. It is interesting to notice that 

 many of these creatures pass their lives hidden in holes in rocks, or sunk in mud 

 or sand, where their gorgeous colour is concealed, and, as far as we can see, is of 

 no use to the animal. 



(III.) The papillae. These are, as a rule, wart-like elevations, scattered more or 

 less uniformly over the surface of the body. In a few cases they show a tendency 

 to arrange themselves in rows, but this is rare, and their specific importance is on 

 the whole small. 



1 Published also in the Recueil Zool. Suisse, Vol. m. p. 313. 



