748 . W. P. SLADEN ON LEPIDODISCUS LEBOURI FROM 
cleared away. The whole organism, as usual in most of the remains 
of Agelacrinitide yet found, is much flattened, a circumstance which 
renders it difficult to say what was the exact form presented by the 
body when in hfe. ‘That its dorsal surface was more or less convex 
or subconoidal is beyond doubt; and itis also extremely probable that 
in the present type of Lepidodiscus, at least, the hard test was to a 
certain degree flexible and collapsible: hence the fair deduction 
follows that the animal would doubtless have astonished its captors, 
if there had been dredgers in those early seas, as much as Asthe- 
nosoma (= Calveria, Wy. Thomson) did by its palpitations when first 
hauled on board H.M.S. ‘ Porcupine’ during the expedition in 1869. 
The imbricating scale-like nature of the plates would alone naturally 
lead to this conclusion ; and the presumption is further strengthened 
when the manner is noted in which the spirally disposed radii are 
displaced and contorted under the action of the flattening to which 
the test has been subjected. In addition to this it should not be lost 
sight of that the form of the plates of the radial series likewise fur- 
nishes strong evidence in favour of such aview; for the arched margins, 
the bevelled ends, and the blank interspaces are all provisions calcu- 
lated to afford flexibility; and although the property, it is true, might 
be possessed only to a very limited degree by the radu taken as a 
whole, it would nevertheless be sufficient, in all probability, to corre- 
spond with the movement of the disk-plates—a concord, it may be 
noted, without which the utility of the imbrication of the latter 
would seem very remote. 
Some American paleontologists remark on what they haye con- 
sidered to be traces of pores (presumably of ambulacral function 
from the manner in which the statement is made), situated between 
the plates of the radial series; but in no instance that I am aware 
of have such pores been actually discovered. There is certainly 
nothing of the kind in the Northumberland specimen; and I would 
suggest, without slighting in any way the observations just alluded 
to, the possibility that the blank interspaces which have been 
described in ZL. Lebourt as situated at either end of the line of 
junction of the ray-plates may have been mistaken for true tenta- 
_ cular foramina—an error which might easily occur if the specimen 
had only been imperfectly cleared. 
The early writers on Agelacrinitide regarded the mouth as opening 
on the central portion of the dorsal surface, at the junction of the 
radii, although none of the fossils then known were in a condition 
to prove whether an orifice existed or not. This view must now be 
considered erroneous, as several of the recently discovered specimens, 
which are more perfectly preserved, show unmistakably that no such 
orifice was present on the dorsal surface. The fossil now under 
notice is closely plated in the centre of the disk, and certainly 
possessed no external aperture in that region of the test. 
The orifice situated in the large interbrachial area was referred to 
by Forbes (loc. cit.) as the “ ovarian pyramid;” this opinion has been 
followed by numerous writers up to the present time, whilst others 
have considered it to function as mouth or mouth-anus respectively. 
