258 PLEUROSIGMA. 



var. curvula Grun. ! (Arct. D., p. 60; H.V.H. Atl., pi. 21. f. 3-5* ; 

 Type No. 185), plate 7, fig. 279. 



Narrow, linear, scarcely lanceolate. Transverse striae 21 to 22*5 in 1 

 c.d.m. ; longitudinal striae 24 or 25 in 1 c.d.m. Length, 8 to 12 c.d.m. 

 Breadth, 09 to i'i c.d.m. 



Brackish water. Tete de Ftandre (Scheldt) at Antwerp (P. Gam). 



PI. tenuissimum. W. Sm. (S.B.D. i., p. 67, pi. 22, f. 213*), 

 plate 28,tfig. 798. 



Very small, excessively narrow, feebly sigmoid, with very acute apices. 

 Longitudinal striae, 24; transverse striae, 18 or 19 in 1 c.d.m. Length, 14 

 c.d.m. Breadth, 07 c.d.m. 



Marine. Essex (W. Sm.), Liverpool (Comber; Stolt. ), Hull (Norman), England. Ireland 

 (O'Meara). 



aa. Valves with apices rostrate produced. 



PI. Parked Harrison. (Q.J.M.S., i860, p. 104 ; h.v.h. Atl., pi. 



21, f. 10*; Type No. 190), plate 7, fig. 280. 



Valve rather broadly lanceolate, with acute apices, longly acuminate 

 rostrate, rostrum broad. Raphe dividing the apices of the valve into unequal 

 moieties. Transverse striae about 19 in 1 c.d.m. Longitudinal striae about 

 22 in 1 c.d.m., forming, near the middle of the valve, flexed lines, producing 

 ellipses by their intersections. Length, about 8 c.d.m. 



P'resh water. Rare. Pond in the Park at Antwerp. Canal at Hasselt (Van den Born). 

 England, 



Prof. Cleve considers this form to be a simple variety oi P. distortum. 



PI. distortum W. Sm. (Ann. N.H., 1852, p. 7, pi. 1, f. 10; 



Perag., p. 8, f. 32*), plate 28, fig. 799. 



Differs from the last by its feebly tapering rostrate apices and its finer 

 striae, the longitudinal numbering 28 and the transverse 26 in 1 c.d.m. 

 Length, 6 to 10 c.d.m. 



Marine. England. Ireland. 



PI. Fasciola W. Sm. (S.B.D., i., p. 67, pi. 21, f. 211; H.v.H. 



Atl, pi. 21, f. 8* ; Types No. 191 and 192), plate 7, fig. 281. 



Valve narrow, lanceolate, with apices longly acuminate-rostrate ; strongly 



sigmoid, rostrum very narrow. Raphe dividing the valve into equal moieties. 



Striae rather easily resolved, the longitudinal ones being about 23 and the 



transverse about 21 in 1 c.d.m. Length, about 10 c.d.m. 



Marine. Antwerp (Scheldt), Blankenberghe. England, Ireland, and on all the coasts of Europe. 



