12 BRITISH DIATOMACE.E. 



ordinary forms, which include many others intermediate in size and 

 outline. Conjugation and the formation of sporangial frustules 

 have been observed by Mr. Thwaites and myself in one species of 

 Himantidium. 



Sect. I. Frustules forming a lengthened filament. 



1. Himantidium pectinale, Kiitz. Frustules on F. V. rectangular, 

 straight; V. arcuate, linear, suddenly attenuated towards the ex- 

 tremities, which are slightly produced ; striae 27 in 'OOl". Con- 

 necting membrane obscurely striated ; striae 48 in # 00l". Length 

 offrustule -0007" to -0058". Breadth of valve -0004". v.v. 



Kiitz. Bacill. xvi. 11. ad sp. authen. quae dedit am. De Brebisson. Raben. 

 Siissw. Diat. 1. 1. C. Conferva pectinalis, Dill. Conf. pi. xxiv. ad 

 specim. authen. in herb. Grev. Fragilaria pectinalis, Ag. Syst. p. 7. 

 Ag. Consp. p. 62. Lyng. Tent, lxiii. D. ? English Botany, pi. 1611 ? 

 Grev. B. F. p. 403. Harv. Man. p. 197. Ralfs, Ann. xii. 2. fig. 3 C. 

 ad specim. authen. in herb. Jenn. Hass. Alg. xcv. 1 & 2 b. Quek. 

 H. C. xii. 15. In conj. Thw. Ann. vol. xx. pi. xxii. A. Eunotia de- 

 pressa, Kiitz. Bacill. xxix. 39 & xxx. 2. Himantidium minus, Kiitz. 

 Bacill. xvi. 10. ad specim. authen. quae dedit am. De Brebisson. Con- 

 ferva lucens, Thore, et C. bronchialis, Roth., ad specim. authen. q. d. cl. 

 Dr. Arnott. 



Fresh water. Wareham, Mar. 1848. Cook's Bridge, Sussex, Jan. 1853, 

 W. Sm. Tunbridge Wells, Oct. 1844, Mr. Jenner. Woodhead, Cheshire, 

 May 1852, Mr. T. Brittain. Aberdeenshire, Dr. Dickie. Cader Idris, Mr. 

 Capron. Dolgelly Earth, Lough Mourne, and Lough Island Reavey and 

 Mull Deposits. (Falaise, M. De Brebisson. Pic de Sancy, Auvergne, elev. 

 6000 feet, June 1854, W. Sm.) 



Plate XXXII. 280. 



2. Himantidium undulatum, W. Sm. V. arcuate, constricted near 

 the extremities, with a central inflation on the concave surface, 

 and one or more dorsal elevations ; striae 22 in *00l". Length of 

 frustule -0021" to -0058". Breadth of V. -0002". v.v. 



Fragilaria pectinalis, var. /3. undulatum, Ralfs, Ann. vol. xii. pi. ii. fig. 3 d. 

 Hass. Alg. xcv. 2 d. Eunotia nodosa, Ehr. Microg. passim. 



Fresh water. Maam, Galway, July 1853. Lough Avaul, Co. Cork, 

 June 1855, W. Sm. Sussex, Mr. Jenner. Newcastle, Co. Down, Mr. W. 

 Thompson. Island of Arran, Dr. Arnott. Quenmore, Lancashire, Mr. Johnson. 

 Haverfordwest, April 1 854, Mr. Phillips. Lough Island Reavey and Mull 

 Deposits, Dolgelly Earth, &c. 



Plate XXXIII. 281, varieties 281 a, a', and a 2. 



