278 Remarks on the Retina. 
Alabama are the Plagiostoma dumosum, Pecten perplanus, P. Poul- 
soni, Nummulites Mantelli, and Scutella Rogersi. The limestone of 
the upper division is very light colored and een sometimes friable, 
in other instances more compact. 
The Medial division is chiefly recognised in Gloucester and Bur- 
lington counties, New Jersey, and near Wilmington, N. C. It is of- 
ten of astraw yellow color, hard, compact, and either subcristalline 
or granular, or even friable. Its characteristic fossils are Spatangus 
parastatus, Ananchytes fimbriatus, A. cinctus, Nucleolites crucifer, 
Belemnites ? ambiguus, Scalaria annulata, and Cidarites diatretum. 
The Lower division, or green or ferruginous sand, is too familiar 
to need any additional comment, often underlying the other divisions, 
and often again entirely denuded and exposed. Stretching from New 
Jersey in the form of a crescent through the southern States, it is 
readily traced into Arkansaw and Missouri, and is every where char- 
acterized by fossils described and figured in my Synopsis. 
I have thought the above facts might; interest those of your readers 
who live in the vicinity of the Sasil strata, which are well worthy 
of their patient research. 
Arr. XV.—Remarks on the Retina; by W. C. Watuace, M. D. 
Surgeon to the N. Y. Institution for the Blind. 
Iris stated by some of the older anatomists that the retina i of a 
fibrous texture, yet no mention is made of the manner by which the 
fibres may be exhibited. By modern authors it is asserted to be @ 
mere pulpy mass without fibres. 
That the retine of fishes possess a fibrous appearance is stated by 
Cuvier. The fibres may be seen in the skate, like floss silk, radiat- 
ing in a beautiful manner from the entrance of the optic nerve to the 
ciliary body. After a short immersion in alcohol, they are very con- 
spicuous in the streaked bass, the cod, the halibut, and the poigee- 
Exterior to the fibres there is a layer of pulpy matter. 
After the eye of an ox is immersed for a day in alcohol, the ante- 
rior portion and the vitreous humor then removed, and a solution of 
corrosive sublimate poured into the cup that remains, by separation 
with a hair pencil the fibres may be demonstrated, radiating from the 
optic nerve to the ciliary body. The central artery and vein of the 
retina dividing into branches may be seen above the fibres, but by 
this dissection there is no appearance of membrane connecting the 
