BRITISH DIATOMACEiK. 103 



Navicula dubia, Kiitz., Greg. I.e. fig. 3. 



„ Bacillum, Ehr., Greg. /. c. fig. 4. 



„ lacustris, Greg. Mic. Journ. vol. 4. pi. i. fig. 23. 



„ lepida, Greg. I.e. fig. 25. 



„ incurva, Greg. /. c. fig. 26. 



„ longiceps, Greg. /. c. fig. 27. 

 Pinnularia varians, Greg. F. mutabilis, Greg. Mic. Trans, vol. iii. 

 p. 10. pi. ii. figs. 1-33. 



la the paper quoted, Dr. Gregory figures and describes a number of forms 

 under the above names, which vary greatly in the outline and size of their 

 valves, but are all referred by him to two typical modes of striation, viz. Pin- 

 nularia varians, with 14 to 18 striae in •001", and P. mutabilis, with 24 to 26 

 striae in - 001". In his remarks on these species, Dr. Gregory seems disposed 

 to consider that form and size are not to be regarded as of specific importance, 

 justly observing, " that the more the Diatomacese are studied, the more do 

 we perceive that in many species the shape or outline is subject to endless 

 variations." 



In the absence of any specific descriptions of P. varians and P. mutabilis, 

 I must therefore conclude that the characters Dr. Gregory attributes to these 

 species are to be sought for in the striation only ; and as these correspond 

 to those given in the Synopsis to Navicula Semen, N. tumida, Pinnularia ob- 

 longa, P.peregrina, P. acuta, P. radiosa, &c, I feel obliged to conclude, that 

 all the forms included under P. varians and P. mutabilis may be referred to 

 one or other of the species I have just mentioned. 



Pinnularia exigua, Greg. Mic. Journ. vol. 2. pi. iv. 14 = P. muta- 

 bilis, Greg. Mic. Trans, vol. 3. pi. ii. 18 b. 

 Pinnularia parva, Greg. /. c. fig. 1 1 . 



„ apiculata, Greg. Mic. Journ. vol. 3. pi. iv. 21. 



„ Gastrum, Ehr., Greg. Mic. Journ. vol. 3. pi. iv. 20. 



„ megaloptera, Ehr., Greg. Mic. Journ. vol. 4. pi. i. 6 = 



P. lata, Synop. xviii. 167? 

 Pinnularia Dactylus, Ehr., Greg. Mic. Journ. vol. 4. pi. i. 1 = P. 



viridis, Synop. xviii. 163? 

 Pinnularia pygmsea, Ehr., Greg. Mic. Journ. /. c. fig. 8. 



„ linearis, Greg. /. c. fig. 29. 



„ digito-radiata, Greg. /. c. fig. 32. 



„ suhcapitata, Greg. /. c. fig. 30. 



„ Elgensis, Greg. /. c. fig. 33. 



„ globiceps, Greg. /. c. fig. 34. 



