156 rOSSIL SHELL. 



jPLOEILLUS. Montf. A genus of microscopic Foraminifera. 



ELUVIATILE. (Fluviatilis.) Belonging to a river or running 

 stream. Ex. Limnaea fluviatUis. 



FLUVIATILE CONCHACEA. See Conchacea. 



EOEGrlA. Gray, 1840. Aspeegilltim. Novae Zelandisa. 



FOLIATED, or FOLIACEOTJS. (Yvom folium, a leaf.) When 

 the edges of the successive layers of which a shell is composed 

 are not compacted but placed apart from each other, projecting 

 like tUes, the shell is said to be of a foliated structure. The 

 common Oyster, fig. 180, presents a familar example. 



FOEAMINIFEEA. D'Orb. (Fora?wew, a hole or pit) An order 

 established for minute many chambered internal shells, which 

 have no open chamber beyond the last partition. Lamarck, 

 D'Orbigny, and other writers have placed them among the 

 Cephalopoda in their systems, but Du Jardia, on comparing the 

 fossils with some recent species of the same class, arrived at the 

 conclusion, now generally adopted, that they constitute a dis- 

 tinct class, much lower in degree of organization than even 



' the Eadiata. Not recognizing these microscopic bodies as shells, 

 properly so called, but considering them sufiiciently numerous 



■ and interesting to form a distinct branch of study, I do not 

 think it desirable to describe the genera, or to present any 

 arrangement of them in this work. 



FOENICATED. Arched or vaulted, as the exfoliations on the 

 costso of Tridacna Elongata, fig. 157. 



FOESAE. Gray, 1840. Is it not a Trichotropis ? 



FOSSIL SHELL. A shell is considered to be in a fossil state 

 when, the soft parts having ceased to exist, it is deprived of all 



• its animal juices, has lost all, or nearly aU its natural colour, and 

 is thus changed in its chemical composition, when little or nothing 

 is left but a mere bone, which is embedded in a sedimentary 

 deposit. In this state it is fragile, prehensible to the tongue, 

 and either destitute of colour or tinged with the diluted mineral 

 matters which pervade the stratum in which it lies. In some 

 cases, the mineral composition of the shell is so completely 

 changed as no longer to present its proper structure, consisting 

 of successive oblique layers of shelly matter ; but is altered into 



