in the Neighbourhood of Edinburgh. 181 



Nautilus, but we are totally precluded from identifying it with 

 /f^K smh tnat c ^ ass °^ Mollusca, as the internal constitution of 

 ■^w \J* its shell shews no septa whatever ; but, on the con- 

 ° ° 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, invites 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, Lycopodiaceae, 

 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 



