O'Meara — Report on the Irish Diatomacece. 403 



ends, moniliform, the beads being quadrangular ; length '0040, 

 breadth -0012; breadth at the constriction -0007. (Plate 33, fig. 30.) 

 Gregory, Q. J. M. S., 1856, PI. v., fig. 14. Ealfs, in Priteh., 

 p. 893. Rab. Fl. Eur. Alg., sect, i., p. 204. — ISTavicula entomon. 

 Donkin, N. H. Brit. Diat., p. 49, PI. vii., fig. 5. The outline of this 

 form greatly resembles that of IS^avicula incurvata, which Kabenhorst 

 makes a variety of this species. So different, however, is the character 

 of the striae, that they cannot properly be considered as nearly related. 

 The present form differs so much, both in outline and striation, from 

 !N^avicula entomon, that it ought to be considered a very distinct 

 species. 



AiTan Islands, Co. Galway. 



Naviaila gregorii, (O'Meara). Marine. 



Yalves considerably constricted, lobes much expanded, median 

 compartment wide, greatly inflexed at the ends, slightly constricted 

 in the middle ; central nodule large, quadi-angular, with three short 

 spine-like projections at each side ; compartments on either side nar- 

 row, attenuated to a point at the ends, roundly expanded in the mid- 

 dle ; marginal band of striae wide ; stria9 convergent in the middle, 

 radiate towards the ends, moniliform ; beads large, qaadi'angular ; 

 length '0045, breadth -0028 ; breadth at the constriction -0016. 

 (Plate 33, fig. 31.) 



ISTavicula didyma, var. y. Gregory, Q. J. M. S., 1856, p. 45, 

 PI. v., fig. 16. 



Arran Islands, Stomachs of Ascidians, Eoundstone Bay, Co. 

 Galway. 



Nmicula wiUiamsonii, (Wm. Sm.) Marine. 



Talve large ; margin incurved, rather than constricted ; median com- 

 partment wide, infiexed at the ends, constricted in the middle ; com- 

 partments at either side scarcely so wide as the median one, narrowed 

 to a point at the ends, greatly expanded, and anglewise in the mid- 

 dle, striate ; marginal band of striae wide ; striae slightly convergent 

 in the middle, radiate towards the ends, moniliform ; beads large, 

 quadrangular ; length "0072, breadth '0029 ; breadth at the middle 

 •0026. "(Plate 33, fig. 32.) 



ITavicula didyma, sporangia! var. ? Wm. Sm., B. D., Vol. i., 

 p. 53, PI. xvii., fig. 154*. — JN'avicula smithii, Donkin, IST. H. Brit, 

 Diat., p. 6, PI. i., fig. 4. This form on first view would appear to be 

 an incurved variety of Navicula fusca, which it resembles much more 

 than it does Navicula smithii. I believe it is only necessary to see 

 the form, which is extremely rare, in order to be convinced that it is 

 as distinct from Navieula didyma as it is from jS^avicula fusca. Pro- 

 fessor Smith informs us that the species came under his observation 

 in a collection made by Professor Williamson in the Isle of Skye. 



Arran Islands ; Stomachs of Ascidians, i^t ii iflstone Bay, Co. Galway. 



