338 PLAGIOGRAMMA. 



P. Gregorianum Grev. (Q.J.M.S., 1859, vii., p. 208, pi. 10, f. 1 

 and 2; H.V.H. Atl., pi. 36, f. 2*; in Type No. 104), plate 10, fig. 390. 



Valve oblong lanceolate, with hyaline median portion showing an elongated 

 pseudo-ocellus, bordered with two robust costae, apices showing a large smooth 

 space. Striae 9 in 1 c.d.m., formed of coarse puncta, sub-quadrangular, 

 forming longitudinal lines ; girdle face quadrangular, obtuse. Length, about 

 2 to 4 c.d.m. 



Marine. Blankenberghe. England (Stolt. ), Scotland (Greg. ), Ireland (O'M.), France (Breb. ), 

 Bahnsie (Lagerst), Denmark (Heiberg). 



P. Van Heurckii Grun ! (h.v.h. Atl., pi. 36, f. 4 *), plate 10, 

 fig. 391. 



Valve narrowly lanceolate, with apices generally somewhat rostrate capitate, 



smooth, with a narrow hyaline transverse band bordered with two costae, far 



from robust; strias 1 1 or 12 in 1 c.d.m., formed of small puncta, forming 



longitudinal lines. Girdle face very slightly constricted from the middle to 



underneath the apices, which are dilated truncate. Median portion only 



showing one robust costae, formed by the nearness of the apex of the two 



costae visible on the valve. Individuals united in rather long filaments. 



Length, 1*5 to 4*5 c.d.m. 



Marine. Found on one occasion on a jetty between Heyst and Blankenberghe, and at another 

 time in the mud sediment ot the second Basin at Blankenberghe. Surface of the River Dee, 

 England (Stolterfoth) 



COHORT OF TABELLARIINE^. 



ANALYSIS OF TRIBES. 



f Frustules genuflexed ...... Entopylese. 



Frustules 

 not as 

 above. 



( Valves pyriform (more or less in the shape of a pear) that is 



cuneate-oval ..... Licmopliorese. 



f Frustules forming a spiral band . . Meridionese. 



Valves not /False septa very distinct, seldom 



as above. "| Frustules J reduced to knobs . . TaPellariese. 



I not spiral. J 

 ^ v False septa usually absent . DiatomeEe. 



Tribe XL Entopyle^:. 



Frustules showing rudimentary septa (diaphragms) ; valves furnished with 



costee ....... Entopyla. 



Frustules without internal septa ; valves furnished with costae . . Gephyria. 



