442 MELOSIRA. 



M. Jurgensii Ag. (Syst. Alg., p. 9 ; M. subflexilis IV. Sm.; H.V.H. 

 Atl., pi. 86, f. 1-3 and 5* ; Type No. 460), plate 18, fig. 612. 



Differs from the preceding by its more elongated frustules and its valves 

 more convex, and very constricted near the margins. 



Brackish water. Belgium, Holland, England, Germany, etc. ; Scotland (Kitton in Baxter 

 Coll., No. 3846). 



var. octogona Grun. ! (H.V.H. Atl., pi. 86, f. 9*; in Type No. 

 460), plate 18, fig. 613. 



Connecting zone with blunted angles. 



Brackish water. Austruweel near Antwerp. Mixed with the type-form. 

 ** Junction surfaces of frustules plane, often denticulate. 

 I. FRUSTULES SHOWING A SULCUS AT THE SUTURAL MARGIN. 



M. Roeseana Rabenh. (Alg., Nos. 383 and 504, Sussw. Diat, 



pi. 10; Oithosira spinusa //'. Sm. ; H.V.H. Atl, pi. 89, f. 1-6*; Type No. 

 465), plate 19, fig. 614. 



Valves circular, with striae radiant, punctate, puncta becoming more and 

 more fine towards the centre, which is hyaline, and furnished with two to five 

 coarse granules; striae on the margin of the disc about 7 in 1 c.d m. Frus- 

 tules with valves constricted towards the disc, whose margins are denticulate, 

 and having near the sutural margin a broad and deep sulcus. Connecting 

 membrane very finely striate, about 21 striae in 1 c.d.m. Diameter of valve, 

 1 '25 to 4*5 c.d.m. Sporangial frustule almost spherical. 



On moss, etc. Frahan (Delogne), France (De Brb. ), England (W. Sm.), Scotland (Kitton in 

 Baxter Coll., No. 3850), Ireland (O'Meara). 



var. spiralis (Liparogyra spiralis Ehr. ; H.V.H. Atl., pi. 89, f. 7 and 

 8*; in Type No. 465), plate 19, fig. 616. 



Frustules narrow and very elongated, furnished internally with a spiral 

 band transversely striate. 



With the preceding. Very rare. Norwich, England (Kitton). 



M. distans KlitZ. (Baa, p. 54, pi. 2, f. 12; H.V.H. Atl., pi. 86, 

 f. 21-23*; Type No - 4 6l )> plate 19, fig. 616. 



Valve circular, with sparse, rather strong puncta. Frustules with very 

 thick valves, sulcus rather broad, but very deep. Striae, 14 in i c.d.m. 



Fresh water. Hatrival (Del.). Found throughout Northern Europe. 



