J. Lawrence Smith on the Inverted Microscope. 233 
(Catenipora escharoides), and Strombodes striatus, Milne Ed- 
wards, fossils characteristic of the Niagara and Onondaga lime- 
stones, and in America never found in the lower rocks; wit 
these occur Atrypa reticularis in plenty, a Terebratula with three 
raised plaits, and very rarely a Leptena or Strophomena. 
two spiral shells recall the shapes of some of Hall’s species of 
Holopea, but are too imperfect for identification ; and there is a 
long spiral shell, like Murchisonia gracilis. Encrinurus punc- 
tatus is the only trilobite. 
The most striking shell, perhaps, is a species of Ormoceras, 
the short broad siphuncles of which are well preserved, while the 
shell has decayed, and these so much resemble those figured by 
Dr. Bigsby and Mr. Stokes in the Geological Transactions, second 
series, vol. i, pl. 30, figs. 4, 5, 6, 7, that we think there can be no 
doubt of their identity. And it is very interesting, as bearing no 
the question of age, that these were found at Drummond Island, 
the only limestones of which are Upper Silurian, 
Indeed the whole aspect of this collection, small as it is, is as 
strikingly Upper Silurian as that of the former one was Lower . 
Silurian. The preponderance of the Catenipora, Favosites and 
Stromatopora, &c., is characteristic of the higher rocks, and they 
are associated with Pentamerus oblongus (the characteristic fossil 
of the Clinton group, which may be regarded as the base of the 
upper division), and this shell in America is far more limited in 
its vertical range than it is in Britain. 
Arr. XXVII.—The Inverted Microscope—a new form of Micro- 
Scope ; with the Description of a New Eye-piece Micrometer, 
and a New Form of Goniometer for Measuring the Angles of 
Crystals under the Microscope; by J. LawRENcE Smrrn, M.D., 
Professor of Chemistry in the University of Louisiana. 
Tue instrument forming the subject of this article, was invented 
the same year; and, with additional improvements in the microm- 
eter movement, was laid before the American Scientific Associ- 
ation in 1851. Besides the mention made of this instrument in 
this T now hasten to do, in justice to myself, since seeing in the 
last edition of Quekett’s work on the Microscope, a short descrip- 
tion of this instrament under the title of Nachet’s Chemical Mi- 
ope. How it is that my name has been entirely omitted in 
connection with it, is a mystery to me; it must have arisen 
Sscoxp Serres, Vol, XIV, No. 41.—Sept., 1852. 20 
