DONKlNj ON DIATOMACE.^. 9 



quadrangular, constricted laterally; S. V. linear elliptical, 

 extremities rounded; valve convex, compressed laterally, with 

 an imperfectly orbicular stauros not reaching to the margin ; 

 striae coarse, moniliform, monilae irregular elongated. Length, 

 from -0025" to -0350" ; breadth, from -0008" to -0010 ". 



This species I have named from the hourglass-shaped out- 

 line of the F. V. ; it is a very abundant littoral form, being- 

 present in the greater number of gatherings I have made 

 from time to time on the Northumbrian shore ; it is very 

 little subject to variation in outline and striation ; and though 

 closely allied to Stauroneis pulchella, it diflfers from that 

 species in being a much smaller form, in the outline of the 

 F. v., in the much greater convexity of the valve, in its 

 striation, and size and shape of the stauros. The var. of 

 S. pulchella, figured by Professor Smith {' Synop.,^ vol. i, 

 pi. xix, fig. 194, b), is common on the Northumbrian shore, 

 and seems to take the place of the typical form, which is 

 rare. 



Hab. Cresswell, Druridge Bay^ Tynemouth ; coast of 

 Normandy, De Brebisson. (^(-Ct, * H / 



4. Navicula truncata, n. sp. — Form on F. V. rectangular, 

 constricted laterally, angles truncated. On S. Y. narrow^, 

 linear elliptical ; extremities subacute ; valve convex, com- 

 pressed laterally ; striae costate, coarse, parallel, reaching 

 nearly to the median line. Length, from •0025" to *0035" ; 

 breadth of S. V. about -0005". 



Hab. Boulmar Baj^, Druridge Bay, Cresswell, Tyne- 

 mouth, abundant. Frith of Clyde, the late Professor 

 Gregory. {\^^ Sj 



5. Navicula Northumbrica, n. sp. — Form on F. V. broad, 

 quadrangular, with gently rounded angles, and slightly con- 

 stricted laterally ; striae delicate, moniliform ; those opposite 

 and on either side of central nodule coarse and opaque, 

 forming a dark bar, extending from nodule towards the 

 margin of valve; valve highly convex, and compressed 

 laterally, from the margins towards the median line, into 

 a keel. S. V. narrow, lanceolate acute. Length, from 

 •0018" to -0030"; breadth of F. V., from -0012" to -0018", 

 of S. V. -0004". 



The delicate moniliform striae and opaque line opposite 

 the central nodules, as seen on the F. V., readily distinguish 

 this form from its allies. The narrow acute S. Y. is also 

 very remarkable ; for, owing to the valve being so strongly 

 compressed and com^ex, its margins and median line cannot 

 be brought into focus at the same time with a ^-in. or a 



VOL. I. NEW SER. B 



