4 SPH^ERIID^E. 



les Pisidies Francises,' by Dr. A. Baudon of Mouy, may 

 be profitably consulted by those who take a particular 

 interest in this subject. It was published at Paris in 

 1857, and contains fifty-five pages, and five plates of ad- 

 mirably executed figures. All the species of Pisidium 

 described by Dr. Baudon, with the exception of P. co- 

 nicum, appear to be also common to this country ; but 

 one of them (the P. Becluzianum of Bourguignat), which 

 was at that time imperfectly known to the author of this 

 essay, and its generic relation to Pisidium properly ques- 

 tioned by him, happens to be a marine shell, viz. the 

 Turtonia minuta, M. Gassies having procured specimens 

 from Belfast, where it is abundant. 



Genus I. SPILE'RIUM*, Scopoli. PL I. f. 1, 2. 



BODY nearly equilateral : mantle having a double tube. 



SHELL slightly inequilateral ; beaks placed near the centre 

 of the dorsal margin. 



This genus was founded in 1777 by Scopoli (Introd. 

 ad Hist. Nat. p. 397, no. 88) in sufficiently explicit 

 terms, taking the Tellina cornea of Linne as the type ; 

 but Bruguiere (who was followed by Draparnaud and 

 other authors) afterwards proposed for the same genus 

 the name of Cyclas, by which it has been more generally 

 known. Owing, however, to the bibliographical re- 

 searches of Dr. Gray, the older and equally appropriate 

 name of Sphcerium was restored by him in 1847 ; and 

 this latter name has since been adopted by Mbrch, Bour- 

 guignat, and other continental conchologists. The law 

 of priority seems to require the recognition and use of 

 this name. I am aware that in thus advocating the 

 substitution of another (although an older) name for that 



* From its spherical shape. 



