AMPHORA. 137 



7. Amblyamphora CI. Valves without longitudinal lines. Ventral 

 portion rather large, with a structure similar to that of the dorsal 

 portion or striae finely punctate. The branches of the median line 

 diverge from the central nodule. (Type form : A. obtusa). 



ANALYSIS OF SPECIES. 

 ( Strife very distinct, distant ..... A. spectabilis. 



' Strife very delicate, indistinct, approximate . . .A. obtusa. 



A. spectabilis Greg. (Diat. of Clyde, p. J4, pi. 5, f. 80*), plate 



24, fig. 687. 



Frustule linear or linear-oblong with apices rounded, sub-truncate. Valve 

 with apices obtuse, ventral portion rather broad, raphe strongly inflexed, 

 central nodule large. Stria; rather broad, distant, diminishing in breadth from 

 the side of the raphe, 5 to 6 in 1 c.d.m. Length, 8 to 15 c.d.m. 



Marine and brackish water. Coasts of the North Sea; England (Stolterfoth) ; Scotland 

 (Greg.), etc. 



A. obtusa Greg. (T.M.S. 1857, v., p. 72, pi. 1, f. 34; Ad. Sch. 



Atl., pi. 40, f. 16-17*), plate 24, fig. 688. 



Frustule broadly linear-oblong with apices rounded, not truncate. Valves 

 arcuate on dorsal side, almost straight on ventral side, with apices very obtuse. 

 Raphe very inflexed with central and terminal nodules very large. Ventral 

 portion broad, with striation identical with that of the dorsal portion, ventral 

 margin slightly constricted near the apices. Stria; very delicate, approximate, 

 indistinct, about 12 14 in 1 c.d.m. Sutural zone narrow. Length, 8 to 13 

 c.d.m. Breadth of valves, 1/5 to 2 c.d.m. 



Marine. Coasts of the North Sea ; Scotland (Greg. !), etc. 



8. Oxyamphora CI. Valves without longitudinal lines. Ventral por- 

 tion generally very narrow and with striation identical (not finer) with 

 that of the dorsal portion. Raphe generally straight and approximate to 

 margin. Nodule often stauroid. Striae punctate (Type form : A. acuta). 



ANALYSIS OF SPECIES. 



f Frustules with the outer margins more or less inflated at 



the median portion . . . . .A. ostrearia. 



Valve with ] r . , ... f Ra P he straight . A. acuta. 



stauros. 



{ Frustule with 



outer margins -j Raphe gradually inflexed . A. laevis. 



not inflated. 



[ Raphe abruptly inflexed . . A. lsevissima. 



Frustule linear, elongate, subelliptic . . .A. bacillaris. 



f Frustule robust with striae robust, 



Valve with- j Frustule moniliform . . . .A. Arcus. 

 out stauros. \ more or less J 



quadra ngu- j p t 1 f ^aphe straight . A. hyalina. 



I hyaline. "j R ap h e inflexed . A. lineolata. 



