a Genus of Corldculadai. 279 



establishes the genus Musculium, under the following description : 

 " Sumpfershale. Die Schalen gleich, rund, sehliessen iiberall. 

 Das Schloss mit zwei kleinen Zahnen, ohne Seitensdhnen ; Vor- 

 der-und Hinterspalte ziemlich gleich ; das Band auswendig. M. 

 lacustre {Tellina), Gra. p. 3242 ; Ch. vi., f. 13, f. 135." 



The species referred to by Link as typical of his genus (Sphce- 

 rium lacustre) places Musculium under /Sjjhceriian, and not under 

 Pisidium, as stated by Iierrmannsen.* 



Link, in his description of Musculium, commits a grave mis- 

 take in asserting the want of lateral teeth — a character existing 

 in no European fresh-water bivalve. Prof. Morch attributes this 

 error to a misprint. 



H. and A. Adams \ adopt Musculium in the early part of their 

 work, but eventually it is changed to Pisum. 



Etiglesa, Pera, Cordula. 



These three genera were published for the first time in ^1852, 

 though Leach established them 1818-20, on specimens in the 

 British Museum. 



In the description of Euglesa, Leach says : " The umbones are 

 central, or situated a very little behind the middle of the shells ; " 

 and that " The tracheal tubes are exserted." Pisidium being 

 inequilateral and having but one tracheal tube, the species of 

 Euglesa cannot be referred to it, but must be classed under 

 Spkcerwm. 



Jenyns,§ Bourguignat ;| and Deshayes ^[ differ with me, and 

 have placed the single species of this genus, E. Henslowiana 

 under Pisidium. 



Pera and Cordula, from the descriptions given, are simply 

 synonyms of Pisidium. 



* Proe. Zool. Lond., xix., 232, 1851. In several of my papers on the Corbicu- 

 ladie I have made the mistake of mentioning Gray's name in connection with Mus- 

 culium instead of Herrmannsen's. 



\ H. aud A. Ad. Gen., Rec. Moll, II., 1858. 



% Leach, MolL Brit. Synop, edit. Gray, 291, 292. 



§ Trans. Phil. Soc. Cambr., vi., 1832.,. 



\ Rev. Mag. Zool., 1854. 



1 Brit. Mus. Cat. Conchif., 274, 1854.] 



