260 REV. E. o'meara. 



strongly costate, distant. This form at first vieAv might be 

 confounded with Amphora cymhifera, but the costfe in that 

 species are very much finer and closer than in the present. 



Navicula Archeriana, n. s., PI. VIII, fig. 9. — Valve con- 

 stricted ; length -0036 ; greatest breadth -0012 ; breadth at 

 constrictor "0008. Striae marginal costate, parallel in the 

 middle, shghtly radiate towards the apices. A longitudinal 

 line on either side of the median line divides the inner portion 

 of the valve into three compartments without striae. This 

 form had been previously found by me in Ireland, namely, 

 in gatherings by Professor E. Perceval Wright at the Arran 

 Islands, and also in the stomachs of Ascidians from the 

 Coasts of Clare, as well as in stomachs of Ascidians collected 

 in Roundstone Bay, Co. Galway, by A. G. More, Esq. 



Navicula nebulosa, var., PI. VIII, fig. 10. — Valve ellip- 

 tical ; length -0032 ; breadth -0015. Marginal striee obviously 

 costate, not of uniform length as in Navicula nebulosa, Greg., 

 but short in the middle and parallel, gradually lengthening 

 towards the apices, and again becoming shorter as they ap- 

 proach the apices. Median line well defined, slightly en- 

 larged towards the central nodule ; on either side of median 

 line and close to it there is a faint longitudinal line ; between 

 this latter and the marginal band of costate striae the valve 

 is marked with fine moniliform striae radiately arranged. In 

 Nav. nebulosa, with good illumination, similar striae may be 

 detected, but they are parallel, and extending not more than 

 half way between the marginal band of striae and the median 

 line. A row of strong, short costa3 extends along the longi- 

 tudinal lines from the apices about one quarter the length of 

 the valve ; near the apices they are short, gradually increase 

 in length, and then diminish till they vanish. Although 

 this form in its main features so strongly resembles Navicula 

 nebulosa that it could scarcely be considered distinct from it, 

 yet the peculiarities I have noticed are such as are worthy of 

 sj)ecial attention. 



Synedra arctica, n. s., PI. VIII, fig. II. — Valve expanded 

 at the middle and ends ; length '0052 ; striae marginal, 

 finely costate. The valve on front view is linear, with a 

 slight expansion at the ends ; striee marginal. This peculiar 

 and well-marked form occurred with tolerable frequency. 



I have only to add that some specimens were found of a 

 form which at first I was disposed to consider new, but which, 

 upon more mature consideration, I think, is not unlikely 

 identical with Navicula Auklandica, Grun. I was xmable to 

 obtain a front view, so cannot say whether the striae on the 

 connective membrane noted by Grunow in N. Auklandica 



