GALEOMMA. 151 



genera to which they belong. The family of Nayades includes 

 nearly all the fresh-water bivalves ; and the Melaniana and Lim- 

 neana are the principal among univalves. 



FRONDICULARIA. Defr. A genus of microscopic Foraminifera. 



FRONT. The surface of a shell on which the aperture appears. 



FULCRUM. That part of a shell on which any other part rests 

 or turns. The term is applied more particularly to the tumid 

 part in the hinge of bivalve shells on which the ligament is 

 fixed. 



FULGUR. Montf. Pyrula perversa, Auct. and such other 

 species as have an angulated spire. Fig. 388. 



FUSIFORM. (Fusus, a spindle.) Shaped like a spindle, swelling 

 in the centre and tapering at the extremities. Ex, Fusus, fig. 387. 



FUSUS. Brug. (A spindle.) Fam. Canalifera, Lam. Siphono- 

 stomata, Bl. — Bescr. Fusiform, turrited, with many rounded 

 whorls ; aperture generally oval, terminating in a long straight 

 canal ; operculum horny, pyriform. — Obs. The Fusi are subject 

 to considerable variations in form. The recent species are 

 numerous and do not appear to be confined to any climate. The 

 fossil species are also numerous, chiefly abounding in the tertiary 

 formations. The recent species are mostly tropical. Fig. 387, 

 F. Colus. 



GALATHiEA. Brug. Potamophila, Sow. Megadesma, Bowd. 



GALEA. Klein. Purpura, Auct. 



GALEOLARIA. Lam. (From Galea, a helmet or crest.) A genus 

 composed of species of Serpula, Auct. Distinguished as being 

 fixed by the side of the shell, and having the anterior extremity 

 erect, the aperture terminating in a tongue- shaped projection. — 

 Obs, This genus is said by Lamarck to resemble Vermilia in 

 other respects, but to differ in having the anterior part raised. 

 Fig. 6, G. decumbens. Africa and Australia. 



GALEOMMA. Turt. Fam. Pholadaria, Lam.— Descr. Thin, 

 oval, equivalve, equilateral, with the ventral margin gaping ; 

 hinge with one cardinal tooth in each valve; muscular impressions 

 two, approximate ; palleal impression interrupted, not sinuated ; 

 ligament small, partly internal, partly external, fixed on a promi- 



