12 POST-TERTIARY LACUSTRINE SAND 



appear to be characteristic of E. Ralfsii. This latter species 

 occurs with the usual characters ; and I am inclined to regard 

 the form, fig. 11, as distinct, but do not venture to give it as 

 a species without further investigation. It is, in all proba- 

 bility, a marine form. 



Fig. 12. Surirella fastuosa /5. This species is finely deve- 

 loped, insomuch that it might almost be taken for a distinct 

 species. I am disposed, however, to regard it only as a finely- 

 developed S. fastuosa, as figured by Smith, and probably more 

 truly typical than the form he has figured. It agrees well, 

 except in being larger, with Kutzing's figure. It is known to 

 be a marine species. 



Fig. 13. Tryblionella constricta, W. G. This pretty little 

 form is very frequent in the deposit. Its form is that of 

 Cymatopleura apiculata, but it is very much smaller, and has 

 all the characters of Tryblionella. Striae transverse, fine, but 

 distinct. I am informed by Mr. West, that he long ago met 

 with it in gatherings from Poole Bay. It is a marine form. 

 (220.) 



Fig. 14 Amphiprora vitrea, £ ? This fine form is frequent 

 in the deposit. The peculiar arrangement of the median line, 

 with its double curvature, at once strikes the eye. Indeed, on 

 comparing it with the figure of A. vitrea, in the ' Synopsis,' it 

 might be supposed to be a distinct species. But in the mean 

 time, and until further examination, I refer it to the species 

 named. It is a marine species. 



Fig. 15. Navicula birostrata, W. G. This is a well-marked 

 species. Form elliptical, with contracted, slightly produced, 

 somewhat truncate apices. Stria? fine, somewhat inclined. It 

 appears to vary a good deal in size. Habitat unknown. (221.) 



Fig. 16. Navicula rhombica, W. G. This beautiful form 

 is frequent in the deposit. Its form is rhombic, varying from 

 short and rather broad, with obtuse apices, to long and narrow, 

 with acute apices. Stria? fine, rather inclined, quite distinct, 

 even in balsam, which at once distinguishes it from N. rliom- 

 boides. The median line and central nodule are also quite 

 different ; and, in consequence, it differs totally in aspect from 

 N rhomboides, which is also present in the deposit, and with 

 which it cannot be confounded. Habitat not known. (222.) 



Fig. 17. Navicula c/astroides, W. G. This form, when 

 small, has some resemblance to N. pusilla ; but is of much 

 stouter habit, and has a brown colour, even in balsam. Besides 

 this, it occurs much larger, being then more elliptical, while 

 the smaller individuals are often almost orbicular. Striae 

 radiate and inclined. The median line and central nodule are 

 very strongly developed, and the short apices appear as the 



