ORAL AND APICAL SYSTEMS OP THE ECHINODERMS. 205 



single central abactinal plate in the Palseocrinoids (or, at 

 any rate, in the larval stages), ^vhich my views suppose, is 

 merely an inference from the presence of such a plate in the 

 stalked larva of Comatula (See Part I, pp. 374, 379, 382). 

 It is almost needless to point out that its existence is scarcely 

 susceptible of proof. 



4. Since the above essay was written (July, 1878) I find 

 that the opinions expressed by Sir Wyville Thomson and 

 myself regarding Hyponotne have been verified by an 

 examination of the "Challenger " dredgings in Torres Strait. 

 Sir Wyville Thomson determined on the spot that Hyponome 

 is merely a Comatula minus its calyx and arm-skeleton. 

 The " Challenger " collection of Comatula contains many 

 specimens from Torres Strait, as well as from other localities, 

 which exhibit the Hypo7iome-covidi\\ioii more or less perfectly. 

 Some of these are Antedons, and the others Actijiometrce, 

 In the latter the anambulacral plating is very extensively 

 developed, and the resemblance to Spliaronites (first pointed 

 out by A. Agassiz) very complete. 



5. It is possible that the mouth-shields or " first inter- 

 mediate interambulacral pieces " of the Ophiurids are really 

 oral plates which appear late, and ultimately assume a 

 somewhat abnormal position. Similar plates occur in 

 Brisinga (Sars and Ludwig), and INIiiller mentions the 

 existence of unpaired interambulacral plates round the 

 actinostome of other Asterids, but he did not regard them as 

 comparable to the mouth-shields of Ophiurids. 



6. Ludwig (' Ophiuren,' p. 251) makes an alteration in 

 Miiller's terminology which is, I think, unsuitable, as it will 

 only lead to needless confusion. In the Crinoids in which 

 the ventral side is upwards, the plates beneath the water-ves- 

 sel were termed subamhulacral by Miiller ; and as mentioned 

 above, he extended this name to similarly situated plates 

 in the other Echinoderme, while he spoke of the ventral 

 plating of the Ophiurid arms as super amhulacral. Ludwig, 

 however, considers this inconvenient, as the Ophiurids, 

 unlike the Crinoids, have their ventral side dowmwards, so 

 that the ventral plating is strictly subamhulacral. It would 

 be interesting to learn how Ludwig would name the coronal 

 plates of an Urchin. According to his reasoning, these 

 are superambulacral round the apex, but subamhulacral 

 round the mouth, while neither name is applicable to those 

 round the equator of the test. Surely if INIiiller himself did 

 not think it inconvenient to call the ventral plating of the 

 Ophiurids superambulacral, it hardly beseems us to cavil at 

 his nomenclature, especially when the proposed change 



VOL. XIX. NEW SEB. O 



