26 



species ; and Moquin-Tandon has noticed it as Corsican. 

 I have found it also on all parts of the Continent. The 

 variety splendens of Baudon occurs in lakes near Lerwick, 

 and at Balmacarra in West Ross. A monstrosity or 

 distortion of this species, as well as of P. fontinale (var. 

 Henslowana), is sometimes met with, which has the 

 valves constricted or divided by a longitudinal groove. 

 This accidental phenomenon in the typical form of P. 

 fontinale induced M. Bourguignat to consider it a distinct 

 species, and to give it the name of P. sinuatum. It is 

 caused by a laceration or injury of the front margin of 

 the mantle. 



This may be distinguished from all the preceding spe- 

 cies by its rounded outline, much more glossy and iri- 

 descent appearance, and by a few separate and deeper 

 grooves or lines which encircle the beak and are espe- 

 cially perceptible in young shells. This is also the only 

 kind of Pisidium which has the tube funnel-shaped and 

 its outer margin crenulated or plaited. For the dis- 

 covery of this species science is indebted to Mr. Jenyns. 



D. Oblong. 



5. P. RO'SEUM*, Scholtz. 



P. roseum, Scholtz, Schlesien's L. - und W. -Moll. p. 140 ; Jeflr. in Ann. 

 Nat. Hist. s. 3. vol. iii. p. 38, pi. ii. f. 3. 



BODY opaline white, orange-yellow, red, or rose-colour in 

 the upper part: tubeloug, slender, subconical, and truncate at 

 its orifice : foot long, semitransparent. 



SHELL subrhombic, ventricose, thin, very glossy, deeply and 

 regularly striated concentrically : yellowish- white or light 

 horn-colour : epidermis extremely thin : anterior side truncate 

 and sloping abruptly below: posterior side much produced and 

 rounded : lower margin nearly straight : beaks placed con- 

 siderably on one side, rather prominent, but obtuse : ligament 



* Rose-colour. 



