307 



I. Species figured by foreign authors, but new to Britain. 



10. Stauroneis ventricosa, Ehr. 



11. Cocconema cornutum, Ehr, 



12. Gomphonema subtile, Ehr. 



13. Melosira distans, Ehr. 



14. Navicula amphigomphus, Ehr., 



15. „ dilatata, Ehr., possibly 

 varieties of Navicula dubia, not 

 figured by the author. 



and 



1. Eunotia tridentula. 



2. Navicula follis (Trochus ?) Ehr. 



3. „ dubia, Kiitz. 



4. „ Bacillum, Ehr. 



5. Pinnularia megaloptera, Ehr. 



6. „ dactylus, Ehr. 



7. „ nodosa, Kiitz. 



8. „ pygniaja, Ehr. 



9. Stauroneis Legumen, Kiitz. 



II. New Species, observed by others, nearly about the same time as 

 by the author, and named by the Kev. Professor Smith, but 

 still MS. species. 



20. Pinnularia hemiptera, Sm. (not 

 figured.) 



21. Navicula sufflata, Sm. (Auvergne. 



16. Navicula apiculata, Sm. 



17. „ rostrata, Sm. 



18. „ scutelloides, Sm. 



19. Mastogloia Grevillii, Grev. 



Pound in Britain by the author. 



Not figured.) 



III. Species now first described and figured. 



22. Cyrabella (?) sinuata. W. G. 



23. „ turgida, W. G. 



24. „ obtusa, W. G. 

 2o. „ Pisciculus, W. G. 



26. „ Arcus, W. G. 



27. Navicula cocconeiformis, W. G. 



28. „ lacustris, W. G., do. /S. 



29. „ lepida, W. G., do. 0. 



30. „ bacillaris, \V. G. 



31. „ incurva, W. G. 



32. „ longiceps, W. G. 



33. Pinnularia gracillima, AV. G. (va- 



civa, Sm.) 



34. Pinnularia linearis, W. G. 



35. „ biceps, W. G. 



36. „ digitoradiata, W. G. 



37. „ Elginensis, W. G. 



38. „ globiceps, W. G. 



39. Stauroneis obliqua, W. G. 



40. „ dubia, W. G. 



41. „ ? ovalis, W. G. 



42. Surirella tenera, W. G. 



43. Gomphonema insigne, AV. G. 



44. „ ventricosum, W. G. 



45. „ Sarcophagus, W. G. 



46. „ sequale, W.G. 



The following numbers refer to figures of the varieties of Navicula 

 elliptica, Kiitz : — 



47. Navicula elliptica, Kiitz. 1 49. Navicula elliptica, var. y 



48. „ „ var. (3 1 50. „ „ var. J 



The whole of the above species, with the few exceptions above 

 noted, were illustrated by highly finished drawings, made from nature 

 by Dr Greville, and enlarged to a scale of 10,000 times the natural 

 linear dimensions. 



The author concluded by making some observations on the distri- 

 bution of fresh- water Diatoms, and showed by various examples that 

 it is often quite easy to determine the characters of a species, if these 

 be well marked, even when it occurs sparingly or scattered, and that 

 when a form is once noticed, wo are pretty sure to find it soon after 

 in greater abundance. To show the value of minute search, he stated 

 that although most of the above new species occurred in several 

 gatherings, yet in point of fact, nearly the whole of them had been 



