BRITISH DIATOMACEiE. 15 



15. Epithemia gibba, /u7/~. F. V. linear, slightly inflated at centre 

 and extremities ; S. V. linear, obtuse ; striae 36 in '001" ; canaliculi 

 15 in -001". Length -0033" to -0104". v.v. 



Nav. gibba, Ehr. Inf. xiii. 19. Hass. Alg. cii. 4. 

 Ep. gibha, Kiitz. Bacill. iv. 22. 



Eunotia gibba, Prit. Anim. xv, 27. In Conjugation, Thw. Ann. vol. xx. 

 pi. xxii. F. 



Fresh water : frequently entangled in the mucus of Sorospoi^a lirescens, 

 Hass. Wareham, Aug. 1847. Lewes, Oct. 1850, W. Sm. Lough Mourne 

 Deposit. Peterhead ditto. Near Aberdeen, Dr. Dickie. Rescobie, Mr. P. 

 Grant. (San Fiore, Italy; Ceylon, 1851, Mr. Thwaites.) 



Plate I. 13. 



16. Epithemia ventricosa, Kiitz. F. V. elliptical, slightly con- 

 stricted at the ends ; V. with acute extremities ; striae and cana- 

 liculi as in the last. Length -0009" to -0018". v.v. 



Kiitz. Bacill. xxx. 9. Nav. gibba, Ehr. Inf. taf. xiii. fig. xix. 4. 



Fresh or brackish water. "Brooks" near Lewes, Oct. 1850. St. Ouen's 

 Pond, Jersey, Aug. 1852, W. Sm. Near Aberdeen and near Belfast, Dr. 

 Dickie. Peterhead Deposit. 



Plate I. 14. 



Genus 2. EUNOTIA, Ehr. 



Frustules free, oblong; valves arcuate, with terminal nodules and 

 convergent striae. 



Closely allied to the former genus, but easily distinguished by the 

 absence of canaliculi, the delicacy of the strise and the dorsal ridges 

 with which most of the species are provided. The F. V, is also uni- 

 formly linear, and the connecting membrane less fully developed than 

 in many of the Epithemice. Isolated frustules of Himantidium might 

 be confounded with the present species, but Eunotia never forms a 

 tenacious filament, though several frustules may sometimes be found 

 united ; the genera are however closely allied, and with difficulty 

 distinguished from each other. 



1. Eunotia Arcus, W. Sm. V. regularly arcuate, acute, with a 

 slight constriction at each extremity, and inflation in the centre of 



