/ CYCLOCLYPEUS. PART in. 



strongly marked on the exterior of the shell. The 

 segments form a spiral of crescents, smooth on the 

 convex and crenulated on the concave side ; and from 

 the latter threads of sarcode proceed, which pass 

 through pores in the inner margins of the partitions, 

 and unite them into one animal. 



The Polystomella lives in tropical seas ; P. crispa in 

 temperate latitudes, and P. striato-punctata inhabits 

 the polar waters ; the genus is found everywhere. 



Although variety of form without specific difference 

 is characteristic of the Foraminifera, it sometimes 

 happens that identity of external form is accompanied 

 by an essential difference in internal structure. Of this 

 the Cycloclypeus is an instance ; it is a rare species of 

 nummuline, dredged up from rather deep water off the 

 coast of Borneo. The shell is gigantic, some specimens 

 r , being two and a half inches in diameter ; but its mode 

 of growth is the same with that of the most complicated 

 Orbitolite. It consists of three superposed stages of 

 circular discs, each circle of chambers enclosing all 

 those previously formed. However, each segment of 

 the animal being enclosed in its own shelly envelope, a 

 supplemental skeleton, and a radial, vertical and annular 

 system of canals, prove that the two animals belong to 

 essentially different families of Foraminifera. There 

 are many instances, especially in the Eotaline group, of 

 isomorphism accompanied with generic difference ; thus 

 no reliance can be placed on variety of external form, 

 unaccompanied by change of internal structure. 



An attempt has been made in the preceding pages to 

 describe a few species most characteristic of some of the 

 genera of this multitudinous class ; and of those selected 

 a mere sketch of the most prominent features of the 

 animal and its abode is given, that some idea may be 

 formed of the wonderfully complicated structure of 

 beings, which are mostly microscopic specks. Yet the 

 most minute circumstances in the forms of the animals 



