10 DONKIN, ON DIATOMACE/E. 



^ objective ; so that the striae can only be examined on the 



F. V. 



Hab. Very abundant on the Northumbrian shore, in 

 several localities, from May to September, 1857, 1858, 

 and 1859. Coast of Normandy, De Brebisson. 



6. Navicula hyalina, n. sp. (fig. 6). — Form on S.V. 

 gracefully elliptical, valve colourless, median line bordered 

 on either side by an opaque, shadowy line, broad, gradually 

 widening on either side of central nodule, and suddenly con- 

 tracting near terminal nodules. Striae very fine and delicate, 

 probably 75 in -0001". 



The gracefully elliptical outline, hyaline appearance'of the 

 valve,' and its striation, more delicate than most of the finely 

 marked Pto<rosi^mcr^a, sufficiently distinguish this species from 

 any of the marine Naviculce with which I am acquainted. It is 

 a severe test-object for the best objectives below a one-eighth 

 inch focus. 



Hab. Cresswell and Boulmar Bay, from July to September, 



1858 and 1859. ^^"dP^ 



7. Navicula cruciformis, n." sp. — Form on F. V. oblong, 

 constricted laterally, extremities truncate. S. V. linear 

 elliptical ; valve convex, compressed laterally, colour brown ; 

 striae costate, about 35 in -001", reaching to median line, 

 absent from centre, so as to leave a stauros reacliing to the 

 margin. Length, about -0030"; breadth of S. V. -0006". 



The marine habitat alone, independent of structural pecu- 

 liarities, distinguishes this species at once from N. Brebissonii, 

 Kiitz. [N. Staicroneiformis, Sm.), which is often gathered 

 at very high altitudes, and which it somewhat resembles 

 in its general appearance. » 



Hab. Boulmar Bay and Cresswell, abundant. ^^> -^^^j " / 



8. Navicula arenaria, n. sp. — Form on F. V. oblong, 

 extremities truncate ; on S. V. narrow, lanceolate, acute ; striae 

 costate, coarse, slightly convergent opposite central nodule, 

 reaching to the median line; length from "0012" to -0012". 



This small form is the most abundant of the littoral 

 species with which I am acquainted, with the exception of 

 N. yregaria, the next form to be described, which, however, 

 is more restricted to certain localities. 



Hab. Boulmar Bay, Druridge Bay, Cresswell, Lyne Mouth, 

 Newbiggin, Tynemouth. ( pl^A 0^ 



9. Navicula gregaria, n. sp. — Form on S. V. broadly 

 lanceolate, apiculate ; striae obscure. 



This exceedingly minute form is very abundant in localities 

 where small streams pass over the sandy beach into the sea^ 



