262 C. A. Young on Recurrent Vision. 
thin translucent substance within. In numerous other instances 
where these basal platforms can be seen still firmly attached to 
their original station, with the plates of the upper side and the 
internal lamellze wholly, or in part removed, the inner, or upper 
side of this platform can be clearly seen to be without a trace 
of a central or other opening, and marked by numerous slender 
radiating lines corresponding to the lamelle of the interior. A 
portion of these strive can be distinctly traced to the central 
point, where, instead of an opening, there is often evena 
minute elevation. It is also worthy of note, that here, on the 
inner surfaces of these basal layers, the little raised radia- 
ting lines, like the lamelle within the disc, do not increase by 
bifurcation, but by the intexcalition of shorter ones between the 
onger; so that if we were to place the specimen mentioned 
above, showing the central opening and striz of its under side, 
on one of these basal platforms, the elevated strive of its under 
side would conform to the little furrows of the platform in such 
a manner that these little furrows would all be closed. 
a 
their bifurcating character would seem to show that they do 
not coincide with the lamelle within, but with the déerstces 
between them; while there are no open slits between these 
strize, as we would expect if they were the edges of lamella, 
but mere furrows. : 
As I have already remarked, if these discs are really bodies 
they must belong to a form constituting the type of a strongly 
marked family of the Cystoidea, if not typical of a more mr 
portant section. 
sane $ 
ArT. XXXIIL—Note on Recurrent Vision ; by Prof. C. A. 
Youne, of Dartmouth College. 
IN the course of some experiments with a new double plate 
Holtz machine, belonging to the college, I have come upon ave 
curious phenomenon, which I do not remember ever to have 
1 
