xiv PERCY SLADEN TRUST EXPEDITION. 
Long before the ‘Challenger’ Report was ready for publication, the collections of 
Asteroidea made by the ‘Knight Errant’ and ‘Triton’ in the Faroe Channel were 
handed to Sladen for examination. It will be remembered that the investigations of 
the ‘Lightning’ and ‘ Porcupine’ expeditions in 1868-9, which paved the way for the 
‘Challenger’ voyage itself, led to the discovery of “warm” and “cold” areas in this 
Channel, but left their physical relation to one another unexplained. The ‘ Challenger’ 
added no direct information on this point, but its observations elsewhere enabled 
Commander Tizard to infer the existence of a solid barrier separating the two areas ; 
and in 1880 he undertook soundings in the Faroe Channel from the ‘ Knight Errant,’ 
which resulted in the discovery of the “ Wyville Thomson Ridge,” with a current 
sweeping over it strong enough, even at a depth of 300 fathoms, to prevent the deposit 
of fine mud or sand. Further observations on the nature and extent of this ridge were 
added in 1882 by H.M.S. ‘Triton.’ The collections made by these expeditions did not 
very materially affect our knowledge of the distribution of the Asteroidea, but the 
‘Knight Errant’ obtained the new genus Wimaster, which, besides being mentioned in 
the general report (12), forms also the subject of a separate paper (13); while H.MLS. 
‘Triton’ produced Rhegaster murrayi, described by Sladen in the ‘Transactions of 
the Royal Society of Edinburgh’ (15), where also is to be found the first detailed account 
of Zoroaster fulgens, named, but only briefly described and imperfectly figured, by 
Wyville Thomson in 1873. 
A summary of the principal features of the ‘ Challenger’ Asteroidea appeared in 1885 
in the “ Narrative” of that Expedition (17); but it was not till 1889 that the complete 
Report was published. Some idea of the magnitude of the task can be gathered from 
the size of the work (more than 900 pages and 118 plates), and from the fact that out 
of 268 species brought home, 184 proved to be new to science; but only those who 
knew Sladen’s capacity for taking pains can form a just estimate of the enormous amount 
of labour which these volumes represent. 
In the arrangement of so large a collection the need for a sound basis of classification 
is obvious. Many attempts to achieve this had been made and are detailed by Sladen 
in his Preface; but the two most satisfactory schemes up to that time were those of 
Perrier and of Viguier. The latter (1878) relied mainly on the character of the 
ambulaeral furrow, and what he called the ‘“ odontophores ” (basal interbrachial plates), 
which he regarded as independent structures. Perrier, however, showed that they were 
morphologically correlated, and in 1884, revising his former work of 1875, insisted more 
than ever on the supreme importance of the pedicellariz in the classification of the 
Asteroidea. Sladen examines these two views, and gives reasons (18. pp. xxii & xxiii) 
for rejecting them both; and he thereupon proceeds to enunciate a system of his own. 
Leaving out the fossil Palzeasteroidea, he finds three sets of characters which permit of 
a binary division of the subclass Euasteroidea, and in each case the individuals belonging 
to the second of the orders so established pass through, during their life-history, a stage 
in which they temporarily present the characters retained through life in the other 
order. ‘Thus (1) we have the papule, which are restricted in area throughout life in 
the Stenopneusia, but spread over the whole body in adult Adetopneusia; (2) the 
