204 Miscellanies. 
ing to this test, unquestionably belonged to the latter class, and that it 
most closely resembled Sphyrena among recent fishes in its dental struc- 
ture. - 
The second instance was the Basilosaurus of Dr. Harlan, which has 
been referred to the class Reptilia; and the double-fanged structure of its 
teeth had, on the strength of its supposed saurian affinities, been adduced to 
weaken the arguments advanced in favor of the mammiferous nature of 
certain fossils from the Stonesfield oolite. Mr. Owen, after describing the 
microscopic character of the teeth of the Basilosaurus, shewed that it de- 
viated from the saurian structure in this respect as widely as the Sauro- 
cephalus, but that the modifications of its dental structure resembled most 
closely that of the Cachalot and herbivorous Cetacea. Lastly, Mr. Ow- 
en alluded to the difference in the views entertained by Cuvier and M. de 
Blainville, ‘as to the affinities of the Megatherium, which was referred by 
the one to the family of the sloths, and by the other to that of the arma- 
dillos; after explaining the well marked differences in the microscopi¢ 
eharacters of the dental structure in these two families of the so-cal 
Edentata, Mr, Owen proceeded to describe the structure of the teeth of 
the Megatherium, and to shew that in its close resemblance to the dental 
structure of the sloths, it confirmed the views of the great founder of the 
science of fossil remains. ‘This paper was accompanied by a number of 
very beautiful illustrative drawings, exhibiting the minute structure of the 
teeth of the animals referred to. 
Mr. Jackson then read a short paper, drawing the attention of the So- 
ciety to a mode of mounting the compound microscope, which differs 
in some particulars from the methods generally adopted. The principal 
object to be kept in view in the construction of the instrument, is the 
prevention of those accidental vibrations which so much interfere with 
microscopic examinations, especially in the neighborhood of crowded 
thoroughfares. This object is effected by connecting together the body 
and the stage of the instrument in such a manner, that whatever vibra- 
tions are communicated to the one shall be equally communicated to the 
other. In the instrument of Mr. J ackson, this principle has been carried 
further than has hitherto been effected ; and it also affords improved fa- 
cilities for minute adjustments, and the accurate admeasurement of mi- 
croscopic objects. 
- A discussion ensued on the subject of Mr. Jackson’s paper, and also 
On the best modes of measuring microscopic objects, and the greater dif 
ficulties encountered in ascertaining the antero-posterior diameters of ml 
nute bodies, as compared with the facilities which we possess of obtaining 
: lateral measurements. The meeting then resolved itself into a conver- 
E ‘Sazione, during which a number of interesting objects were exhibited by 
R Members, many of whom had their microscopes upon the ta 
ing adjo d at 11 o’clock. e 
