198 



NAVICULA. 



Much more frequently found is an elliptic form represented in H.V.H.'s Atl. 

 Supp., f. 23 (plate 4, fig. 151/'), and which constitutes the D. Major of Prof. 

 Cleve. The most essential character of N. Smithii is the double row of beads 

 found between the costae. 



var. aestiva. {N. (estiva Donk. in H.V.H 's Type of Syn., No. 104). 



Differs from the type form with which it is generally accompanied by 

 its more regularly elliptic form and its finer striation. 



Marine. Coasts of England. 



var. scutellum. (TV. scutellum O'Meara, in H.V.H.'s Atl., pi. 9, f. 

 11), plate 4, fig. 152. 



Very small ; valve suborbicular elliptic ; striae about 8 in 1 c.d.m., 

 perpendicular to the raphe at the median portion, then becoming more 

 and more radiate. Length, about 3 c.d.m. Breadth, 2-5 c.d.m. 



Marine. Blankenberghe (H.V.H. , very rare). Ireland (O'M.). 



Observ. When I drew the figure in the Atlas I did not possess the 

 excellent homogenous objectives which have since been invented, and I 

 was consequently unable to recognize the true nature of the striation. Since 

 then I have found that there exists two rows of excessively delicate beads 

 between the striae, and consequently I refer this form, which appears to be 

 the N. scutellum of O'Meara, to N. Smithii. 



N. nitescens Greg. (Diat. of Clyde, p. 15, pi. i, f. 16*), 



plate 26, fig. 747. 



Valve elliptic-lanceolate, with apices subobtuse. Transverse striae, 8 in 

 i c.d.m, cut by the sulcus almost in the middle of their length. Inter- 

 costal spaces showing two rows of small beads well marked in the portion of 

 the valve exterior to the sulcus ; rudimentary and little visible in the internal 

 portion. Length, 5 to 8*5 c.d.m. Breadth, 2 to 3.5 c.d.m. 



Marine and also found in the stomachs of marine animals. Coasts of England, Scotland, 

 Norway, etc. 



N. fusca Greg. (N. Smithii var. fusca Greg. Diat. of Clyde, p. 

 14, pi. 1, f. 15; H.V.H. Atl. Supp., f. 24*: Type No. 105), plate 4, 

 fig- 153- 



This diatom is distinguished from N. Smithii by its generally somewhat 

 smaller size, and because it has only a single row of rather large beads 

 between the costae. 



Marine. Blankenberghe (rare) England, Scotland, Denmark. 



