AMPHORA. 131 



B. Siditral Zone plicate. 



4. Diplamphora CI. Dorsal portion and often also ventral 

 portion with puncta forming longitudinal lines. Puncta coarse. 

 (Type form : A. crassa). 



ANALYSIS OF SPECIES. 



f Valve with double structure ; furnished with costre 

 Valve without I between which are found rudimentary beads . A. crassa. 



an ala . | Valve with structure simple, furnished with three longi- 



^ tudinal curved lines, dividing the valve into two zones A. Grevilleana. 



1. Valve furnished with an ala emanating from the dorsal portion . . A. alata. 



A. crassa Greg. (T.M.S., 1857, p. 72, pi. 1, f. 35 ; Diat. of Clyde, 

 p. 52, pi. 6, f. 94a*) ; plate 24, fig. 675. 



Frustule rectangular, elliptic, with rounded apices. Ventral margin and 

 raphe strongly inflexed at the median portion. Valve with dorsal margin 

 arcuate. Ventral margin concave, inflexed at the median portion. Striae 5 in 

 1 e.d.m., formed of coarse puncta?, arranged in transverse and longitudinal 

 lines. Connecting zone showing lines of coarse punctae, showing the margins 

 of internal segments. Length 8 to 10 c.d.m. 



Marine. Shores of the North Sea : Scotland (Greg.), England (Norm.), Ireland (O'Meara), 

 Finmark (Cleve), etc. 



* Note. The striae of A. crassa have hitherto been inaccurately described by authors. In 

 reality the dorsal margin of the valve shows two rows of strong costa; and at the bottom of the 

 intercostal spaces is a row of delicate puncta. 



A. Grevilleana Greg, (t.m.s., 1857, p. 73, pi. 1, f. 36; Diat. 



of Clyde, p. 50, pi. 5, f. 89 ; Ad. Schm. Atl., pi. 25, f. 41*) ; plate 24, 

 fig. 676. 



Frustule almost oval, with apices slightly truncate. Valves marked with 

 three longitudinal curved lines, dividing the valve into two compartments; 

 apices slightly diminuo-rostrate ; dorsal margin infimtesimally arcuate, ventral 

 margin and raphe inflexed. Transverse striae strong, moniliform, n in 1 

 c.d.m. Sutural zone showing 7 to 8 juxtaposed segments. Length 12 to 

 13 c.d.m. 



Marine. Scotland (Greg.) and various Shores of the North Sea. 



A. alata Per. (Diat. Baie de Villefranche, p. 41, pi. 2, f. n*); 

 plate 24, fig. 677. 



A form distinctly differentiated by the presence of a membranaceous ala, 

 emanating from dorsal portion of the valve. 



Marine. North Sea (Cleve). 



