AMPHORA. 139 



A. acuta Greg. (Diat. of Clyde, p. 52. pi. 6, f. 93 ; Ad. Sch. Atl., pi. 

 26, f. 19 ; 20*) ; plate 24, fig. 692. 



Frustule elliptic, with truncate apices. Valve broad, with dorsal margin 

 regularly arcuate, ventral margin flat. Stauros rather broad, very distinct. 

 Raphe straight. Stride very distinct, distinctly moniliform, 14 in i c.d.m. 

 Length, 8-5 to 13 c.d.m. 



Marine. Scotland ; Greenland ; P'inmark, etc. 



A. laevis Greg. (Diat. of Clyde, p. 42, pi. 4, f. 74 ; Ad. Sch. Atl., 

 pi. 26, f. 8*) ; plate 24, fig. 693. 



Frustule subquadrangular or elongate, with rounded apices, median 

 portion constricted. Valve narrow, arcuate, with apices slightly tapering- 

 rostrate, raphe gradually inflexed, stauros narrow ; stria; fine, 24 in 1 

 c.d.m. Length, 3 to 4 c.d.m. 



Marine. England ; Scotland ; Ireland. 



A. laevissima Greg. (Diat. of Clyde, p. 41, pi. 4, f. 72; H.v.H. 



Atl., pi. 1, f. 15*; Type No. 8); plate 24, fig. 694. 



Frustule linear-oblong, with rounded apices ; excessively hyaline. Valve 

 with raphe abruptly inflexed towards the median portion, with a rather broad 

 stauros. Stria; almost invisible. Length, 5 to 6 c.d.m. 



Marine. England; Scotland; Ireland ; Norway ; Finmark ; probably indigenous to Belgium, 

 but it has not yet been recorded. 



A. ostrearia Breb. ! (in Kutz. Spec. Alg. p. 94; H.v.H. Atl., 

 pi. 1, f. 25*) plate 1, fig. 1. 



Frustule elliptic-oblong, with outer margins inflated at the median portion, 

 apices regularly rounded, sometimes slightly truncate. Valve with raphe 

 strongly inflexed, stauros very distinct, transverse stria; about n in i c.d.m., 

 finely punctate. Connecting zone finely striate, transversely, and showing 

 numerous pleats on the dorsal surface. Length, 6 to 8 c.d.m. 



Maiine. France ; England, etc., probably Belgium, but not yet recorded. 



Sub-var. Belgica Grun. (In H.V.H.'s Type, No. 74). 



Distinguished from A. ostrearia by the outline of the frustules being 

 more quadrate, by the ventral portion of the valves being a little 

 narrower, and by the stria; being closer (16 to 17 in *oi mm. in the 

 middle of the valve) and very finely punctate. Length, '033 "048 mm. ; 

 breadth, - o2i '022 mm. 



Marine. Blankenberghe, washing of sand on seashore. 



