Miscellaneous. te 
studied Unger’s memoir treating of the subject. 5. The Silurian 
assemblage of Fossils, elucidated with the description of a Trilobite ; 
and then follow (6) notes on the Fossils of the Lower Silurian rocks, 
(7) those of the Lingula-beds ; (8) of the Tremadoc Slate; and (9) 
of the Llandeilo Flags; and here we have the modern Ceelenterate 
analogues of the Graptolite well shown in woodcuts; but some 
would like to have their Polyzoan allies shown also. But these are 
_ vexed questions; and altogether, among the fossils of doubtful 
_ alliances Mr. Baily walks delicately; nevertheless he might have 
___ been bolder in referring more of the so-called Annelids and Fucoids 
to crustacean galleries and tracks (as our correspondent Mr. Albany 
- Hancock indicated long ago); and Ribeiria (not Ribieria) might also 
have gone over to the Crustaceans, as Mr. Salter has suggested. So 
_ much for a weak point or two; but we must add that, as this excellent 
work is intended for amateurs and students, as well as for experts, 
_ it would have been advantageous to them if the author had given 
the meanings of the names of the genera and species. This would 
_ be generally of real use in indicating the characters, conditions, or 
history of the things named ; and it would almost always serve in 
_ some way, by association of ideas, to enable the reader and thinker 
to remember both names and things. 
A systematic statement as to the relative abundance or peculiar 
- oceurrence of the several fossils figured would also greatly enhance 
the value of this work. 
With Plate 10 we enter upon the fossils of the Bala-Caradoc 
_ formation ; and’ we look forward with pleasure to the illustration of 
_ the other principal groups of organic remains in this convenient 
shape, which is uniform with Professor Morris’s well-known ‘ Cata- 
logue of British Fossils.’ 
Ba 
MISCELLANEOUS. 
On the Structure of the Eye in the Gasteropoda, and on the Develop- 
ment of the Eyes in the Animal series. By V. Hensen. 
_ Varrovs authors have recently paid attention to the structure of the 
_ eye in the Gasteropoda, and more especially to that of the retina ; 
among them are MM. Leydig, Keferstein, Krohn, Hensen, and 
_ Babouchine. The investigations of these naturalists have clearly 
_ shown that the retina of the Mollusca is divided into an outer and 
_ an inner layer, separated by a thin stratum of pigment. But all 
_ these authors do not agree as to the parts of this retina which are 
_ directly impressed by the luminous waves. Some, particularly M. 
_ Hensen, regard the inner layer as sensible to light; others, on the 
contrary, consider it to be insensible, and that the luminous rays 
_ must pass through interstices of the pigment in order to irritate the 
outer layer of the retina. 
M. Hensen indicates that, in certain theories of vision proposed 
by the most recent authors, the pigment plays an inadmissible part. 
‘Thus, for example, the heat reflected by the pigment has been ad- 
Ann. & Mag. N. Hist. Ser.4. Vol. i. 6 
