BRITISH DIATOMACE.E. 95 



Fresh water. Grasmere, August 1853 ; Co. Cork, June 1855, &c., W. Sm. 

 Mull Deposit ; River Spey ; Lough Leven, and Elchies, Bamffshire, Dr. 

 Gregory. Haverfordwest, April 1855, Mr. Okeden. Near Silverdale, Lan- 

 cashire, December 1855, Mr. Johnson. (Mont Dore, Auvergne, elev. 4000 feet, 

 June 1854, W. Sm.) 



52. Pinnularia hemiptera, W. Sm. Valve linear-elliptical, with 

 rounded extremities ; costae radiate, not reaching median line, 27 

 in -001". Length of valve -0026" to -0036". Breadth of valve 

 •0004" to -0005". v.v. 



Navicula hemiptera, Kiitz. Bacill. xxx. 11. ad specim. authen. quae dedit cl. 

 De Brebisson. 



Fresh water. Parham Park and Rackham Common, Sussex, August 1853 ; 

 Co. Cork, frequent, W. Sm. Falls of the Tummel, July 1854, Dr. Greville. 



A very frequent form in subalpine districts ; often overlooked from its re- 

 semblance to P. viridis, from which it is distinguished by its finer strise and 

 narrower valve. 



53. Pinnularia gracillima, Greg. Valve linear, constricted to- 

 wards the rounded extremities ; striae submarginal, often abbre- 

 viated towards the centre of valve, 27 in *00l". Length of valve 

 •0016" to -0028". Breadth of valve -0002". v.v. 



Var. j3. A larger form with attenuated extremities, v.s. 



Greg. Mic. Journ. vol. 4. pi. i. 31. Grev. Ann. ser. 2. vol. xv. p. 5. Var. (3. 

 P. tenuis, Greg. Mic. Journ. vol. 2. pi. iv. 9. 



Fresh water : often with the last species. Fell-end, Lancashire, Mr. John- 

 son. Var. /3. Mull Deposit; Braemar, August 1854, Dr. Balfour. 



The apparent absence of striae from the centre of the valve, where they often 

 become marginal dots, led me at first to name this species P. vaciva ; but I 

 am now disposed to regard this character as of little importance. The form 

 Navicida pisciculus, Ehr. Kiitz. Bacill. xxviii. 64, is perhaps identical with the 

 present. 



I cannot specifically distinguish var. fl. from the ordinary form. 



54. Pinnularia Polyonca, Breb. Valve with a central and two 

 smaller intermediate inflations ; extremities capitate and rounded ; 

 striae submarginal, 24 in -001". Length of valve -0016" to -0031". 

 Breadth at central inflation -0003" to -0006". v.s. 



Breb. in Kiitz. Sp. Alg. p. 85. ad specimina authentica. Pinnularia undu- 

 lata, Greg. Mic. Journ. vol. 2. pi. iv. 10. 



Fresh water. Mull Deposit, Dr. Gregory. 



