DIATOMACEOTJS DEPOSIT FROM NORTH TOLSTA, LEWIS. 423 



5. Navicula gibba, A. S., Atlas d. Diat., pi. xlv. figs. 50, 51. 

 = Pinnularia gibba, Ehrenb. 



Several specimens. Typical. The costa? on the central side of the terminal 

 nodule extend close up to the raphe for a short distance, as partly but some- 

 what imperfectly indicated in Schmidt's and Smith's figures. 



Length, 01125 mm.; greatest breadth at centre of valve, 0*0125 mm.; 

 breadth of swollen extremities, 0-0105 mm.; breadth in intermediate area, 

 0-0100 mm. Stria?, 10 in 001 mm. 



6. Navicula macilenta, Grun., var. elliptica, nov. (PL XXIX. fig. 4«). 

 = Pinnularia macilenta (Grun.) Ehrenb., var. elliptica. 

 A few specimens of this variety occur. They correspond in most of their 

 characters with the forms figured by A. Schmidt (op. cit., pi. xliii. figs. 7-9), but 

 especially with his fig. 8 as regards the ornamentation of the valve, and with 

 his fig. 7 as regards the disposition of the raphe. The following divergences 

 may, however, be indicated : — (1) The costa? are much more obliquely disposed 

 on the periphery of the central inflation. (2) The terminal hyaline areolae are 

 not subrotund but elliptical, the major axis of this ellipse being directed along 

 the longitudinal axis of the raphe. (3) The raphe is faintly marked, but runs 

 straight throughout its length, its terminal and central extremities being very 

 small. The outlines of the central and circumraphideal hyaline areas agree with 

 those of the specimen figured by A. Schmidt (fig. 8). 



7. Navicula acuta (W. Sm.). 

 = Pinnularia acuta, W. Sm. 



— Pinnularia radiosa, Kiitz., var. acuta, Van Heurck (op. cit., 



pi. vii. fig 19). 

 Fairly common. Typical. Length, 0-0900 mm.; greatest breadth, 0-0100 mm. 



8. Navicula gigas, A. S., Atlas d. Diat., pi. xlii. fig. 1. 



= Pinnularia gigas, Ehrenb. 



Common. The specimens agree in almost all points with the frustules 

 figured by Schmidt. (1) The halo running longitudinally on each side of the 

 valve across the transverse costa? is, however, more clavate in outline at its 

 extremities, showing a slight structural modification in the flexure of the costa?. 

 (2) The terminal hyaline areola? are even more rounded, and upon these the 

 flexed extremities of the raphe present no thickening, but become uniformly 



