in the Neighbourhood of Edinburgh. 181 
Nautilus, but we are totally precluded from identifying it with 
= that class of Mollusca, as the internal constitution of 
Q CG its shell shews no septa whatever; but, on the con- 
S © trary, approaches to that of the Planorbis. It may 
perhaps be considered as a new genus altogether,—referable to 
mollusca. The dimensions of this microscopic animal are two 
or three times those of the Cypris. Its natural size appears in 
the representation inserted below the magnified form. 
The foregoing best defined forms which have come under 
my notice, may for the present suffice. A microcosm of ento- 
mostraca, and. possibly of other classes of animals, mvites the 
attention of the naturalist, among which many undescribed races 
remain to be detected. 
Some of these minute beings have been thus proved to 
possess a structure in common with that of well known en- 
tomostraca, whose habitat is one of stagnant waters rendered 
turbid by decayed vegetables or roots. When these waters are 
dried up by the sun, they still linger within a humid basin, and 
remain there until rains fall anew. 
This habitat agrees with every possible circumstance con- 
nected with the limestone of Burdiehouse,— with the memorial 
of some inland fresh-water lake or tank, within the waters of 
which a calcareous deposit was elaborated, or of some river flow- 
ing sluggishly through a tract overrun with Ferns, Lycopodiacez, 
and such aquatic vegetables, as must have flourished among pri- 
meval marshes. 
The abundance in which these animals appear is the last ex- 
traordinary circumstance to be noticed. 
Although the remains of these entomostraca occur in much 
greater quantity in some parts of the rock than in others, there 
is scarcely a detachable fragment which does not exhibit their 
presence ; and when, during the process of quarrying, a plane of 
stratification belonging to any portion of the limestone bed has 
