MELOSIRA. 441 



Valve circular, very convex, with a rather elevated keel, covered with 

 concentric, undulated striae ; puncta fine (18 to 20 dots in 1 c.d.m.) ; centre 

 smooth. Frustules globular, elliptic, united in pairs, forming a long monili- 

 form filament. Diameter, about 3 c.d.m. 



Marine. Covering the piles of the palisades at Blankenberghe ; England (W. Sm., Norman, 

 Kitton, Arnott, Comber, Stolt.); Scotland (Baxter Coll., No. 2748); Ireland (W. Sm.) ; South 

 Wales (Baxter Coll., No. 2815) ; and on all the Coasts of the North Sea. 



M. Westii W. Sm. (S.B.D., ii., p. 59, pi. 52, f. 333; H.v.H. 



Atl, pi. 91, f. 11 and 12*; in Type No. 320), plate 18, fig. 609. 



Valves circular, strongly convex, with two keels, one marginal, the other 

 near the apex ; external keel surrounded by a circle of puncta in quincunx, in 

 the middle of which, on the internal side of the keel, is found a circlet of 

 coarse beads or small processes, inequally distant, about 2 in 1 c.d.m., 

 excessively fine, centre dull. Frustules globular or subcorneal, solitary or 

 united by twos. Diameter, 3 to 4 c.d.m. 



Marine. Blankenberghe, Antwerp (Scheldt); England (W. Sin., Kitton, Comber, Stolt., Nor- 

 man) ; Scotland ; and probably on all the Coasts of the North Sea, 



M. Borreri Grev. (Hooker's British Flora, p. 401 ; H.V.H. Atl., 

 pi. 85, f. 5-8* ; Type No. 458), plate 18, fig. 610. 



Valves strongly convex, with coarse puncta, between which are found fine 

 puncta irregularly in quincunx, visible only by oblique illumination, about 20 

 rows in 1 c.d.m. ; junction-surface hyaline, sometimes showing some isolated 

 dots. Frustules geminate, very robust, breadth usually more than length. 

 Diameter, 2*5 to 4 c.d.m. Sporangial frustules much larger, about 6 c.d.m. 



Marine and brackish water. Blankenberghe ; England (W. Sm., Kitton, Comber, Stolt., Nor- 

 man) ; Scotland (Dickie, Arnott) ; Ireland (Arnott, O'Meara) ; and on all the Coasts of the North 

 Sea. 



M. varians Ag. (Consp., 1830, P . 64; h.v.h. Atl., pi. 85, f. 10, n, 



14, and 15*; Type No. 459), plate 18, fig. 611. 



Valve circular, almost plane, covered with fine puncta, between which are 

 found some coarse dots. Frustules geminate, with fine puncta, intermixed 

 with some coarser dots, with a row of submarginal, distant, coarse beads. Con- 

 necting zone enclosing two frustules, finely striate. Sporangial frustules almost 

 globular. Diameter, 1-5 to 3*5 c.d.m. 



Fresh water. Very common throughout Europe. 



