INTRODUCTION. xlil 
An account of the “ Asteroidea and Echinoidea of the Korean Seas” (4), published 
in 1879, besides providing some useful notes on the geographical distribution of the 
Echinoderms collected, draws attention to a nomenclature of Asterid pedicellarize by 
Herepath which had been overlooked by Perrier and other recent writers on the subject ; 
and in the same year Sladen described, under the name of Lepidodiscus lebouri (5), the 
first European species of Agelacrinitide from the Lower Carboniferous rocks *. 
By the year 1881 Sladen’s reputation as a careful and accurate worker was so far 
established that he was entrusted by Sir Wyville Thomson with the description of the 
Asteroidea collected by H.M.S. ‘ Challenger’; and as a preparation for this formidable 
task he made, in 1882, a tour of the museums of Europe, visiting practically every one 
which contained any important collection of Echinoderms, and making himself thoroughly 
familiar with their contents. Two preliminary reports on the ‘Challenger’ Asterids 
soon followed, one on the Pterasteridz (11) and the other on the Astropectinidee (14). 
The former affords a most striking illustration of our almost complete ignorance of 
deep-sea forms before that historic expedition, for of thirty-four species of Pterasteridze 
obtained by the ‘ Challenger,’ only two had been already described, while the essen- 
tially abyssal genus Hymenaster, previously known by only one specimen, yielded twenty 
new species, and proved to have a universal distribution in deep waters. Marsipaster and 
Benthaster are also new abyssal genera described in that paper, with two species each. 
In the paper on the Astropectinidze (14), the Porcellanasteride, hitherto little known, 
were included as a subfamily ; but Sladen expressly stated that these advance notices did 
not deal with questions of classification or anatomy (11, p. 189), which were reserved for 
the final report ; and in view of the peculiarities of these Starfishes, we are not surprised 
to find them later on placed in a separate family, together with the genera Styracaster, 
Hyphalaster, and Thoracaster, here (14. described for the first time. 
These Porcellanasteridz present the very remarkable feature of possessing certain 
organs which are entirely unknown in any other family of Asterids. They were 
discovered by Sladen, and named by him “cribriform organs,” while he hazards the 
conjecture that they may act as “percolators”; but nothing is really known of their 
function, nor as to how, if they are of physiological importance, other forms thrive 
without them under apparently similar conditions, while within the family itself they 
vary in number from one to fourteen in each interbrachial arc. Not the least curious 
point about them is that, though occurring in a group of animals (Starfishes) remarkable 
for variation, these cribriform organs are constant in number for each species. We 
thus have: (1) an organ confined to one family, with no clear indication of any structure 
in other families from which it can have been evolved; (2) great variation in the number 
of these organs within the family, coupled with (3) fixity of number within the species— 
truly a most striking combination, and one deserving the attention of all students of 
the Laws of Variation. Unfortunately, practically all the Porcellanasteride are abyssal 
forms, and therefore not available for physiological experiment 7. 
* The type specimen of this is in the Royal Albert Museum at Exeter. 
+ Ctenodiscus, which is doubtfully included in the family, has been found in only 7 fathoms in the North 
Atlantic. It is said to possess a “simplified form of cribriform organ,” but no satisfactory description of this is 
forthcoming (18, pp. 125, 127, & 171). 
e2 
