16 BRITISH DIATOMACEjE. 



Fresh water. Dolgelly, Aug. 1843, Mr. Ralfs. Pentland Hills, April 1821, 

 Dr. Greville. Near Dundee, 1824, Rev. J. M c Vicar. Isle of Arran, 1851, 

 Dr. Arnott. (Pic de Sancy, elev, 6000 feet. Grand Cascade, Mont Dore, 

 elev. 4337 feet, June 1854, TV. Sm.) 



Plate XXXIV. 289. 



2. Odontidium mesodon, Kiitz. V. oval, frequently acuminate ; 

 costa? pervious, from 2 to 4. Length of F. *0005" to -0011". v.v. 



Kiitz. Bacill. xvii. 1. Fragilaria hy emails, Ralfs, Ann. vol. 12. pi. ii. 5. ex 

 parte. Hass. Alg. xcv. 5. ex parte. 



Fresh water. Guernsey, Aug. 1848. Grassmere, Aug. 1853. Moana- 

 rone, County Cork, April 1855, TV. Sm. Aberdeenshire, Dr. Dickie. Meal- 

 bank, Lancashire, April 1853, Mr. G. Smith. Ayrshire, Dr. Arnott, April 

 1854. Elchies, Bamffshire, Dr. Gregory, July 1854. (River Sorgues, Vau- 

 cluse. Genolhac in the Cevennes. Puy de Dome, elev. 3000 feet. Mont 

 Dore, elev. 3425 feet. Pic de Sancy, elev. 6000 feet, June 1854, TV. Sm.) 



Doubtfully distinct from the former, of which it may probably be the 

 immature condition. Odontidium turgidulum of Kiitz. Bacill. xvii. 2. appears 

 to be an intermediate state. 



Plate XXXIV. 288. 



3. Odontidium anomalum, TV. Sm. Filament tenacious; valves 

 linear, constricted towards the rounded extremities ; costae pervious, 

 4 to 12. Length of frustule -0005" to -0022". v.v. 



/3. Frustules with internal cells. 



W. Sm. Ann. ser. 2. vol. xv. pi. 1. 8. Greville, in Ann. ser. 2. vol. xv. pi. ix. 



7, 8, 9. 



Fresh water. Braemar, Aug. 1854, Dr. Balfour. (Genolhac in the Cevennes, 

 elev. 4000 feet, June 1854, TV. Sm.) 



The presence of internal cells, a mode of growth wbich I have noticed in 

 detail in my description of Merldlon clrculare and Himantldlum Solelrolil, 

 and which will again meet us in other cases, is found also to prevail in the 

 present species. Both in the French and Scottish specimens, this variety is 

 in fact the usual condition of the frustules, and the ordinary mode of self- 

 division is only rarely to be met with : tbis has led Dr. Greville, in the paper 

 above quoted, to regard this condition of the frustule as of specific value, and 

 to doubt the propriety of regarding it as accidental or anomalous. It must, 

 however, be remembered that but few specimens of the present species have 

 as yet been discovered, and that a wider comparison will probably substantiate 

 the view I have given, which harmonizes the character of this species with the 

 ordinary Diatomaceous structure. Himantldlum Solelrolil has sometimes 



