EXILAKIA. 433 



This genus bears a slight resemblance to Gomphonema, the 

 frustules being attached in the young state of the species ; 

 they are not, however, triangular, as in the genus Gom- 

 phonema. 



1. EXILARIA CAl'lTATA. 



Plate XCVII. Fig. 1. 



Char. Frustules large. In front view truncate at the ends ; 

 in side view dilated at both extremities into an obtusely 

 pointed head; striated. 

 Ehr. Die Infus. p. 211. pi. xxi. fig. 28. 



This fine and beautiful species I found growing in im- 

 mense quantity in some ditches running parallel to the Barge 

 river near Cheshunt marshes. A few frustules of it have 

 also, I believe, been found by Mr. Ralfs. The frustules in 

 the front view are not to be distinguished from those of 

 Exilaria ulna ; the side view of E. capitata is, however, so 

 distinct, that it would be impossible to confound it with that 

 species. 



2. Exilaria Ulna. 

 Plate XCVII. Fig. 2. 



Char. Frustules large in the fully developed state. In front 

 view slightly dilated at the extremities, and truncate ; in 

 lateral aspect striated, extremities j)ointed. 

 Leuwenhoek's Philosophical Transactions, 1703 (1702), 

 fig. 8. L. K. Bacillaria ulna Nitzsch, Beltriige zur 

 Infusoricnkunde, 1817, p. 99. t. 5. Bacillaria commu- 

 nis Bory, in Diet. Class. 1822. Frustulia obtusa and 

 F. idna Agardh, Consp. Crit. Diatom. Echinclla fasci- 

 culata /3 truncata Greville, 1823 ; Scot. Crypt. Fl. 1. 

 t. xvi. Exilaria fascicidata Greville, 1827 ; Scot. 

 Crypt. Fl. V. f. 291 b. E. truncata Kiitz., in Linna^a, 

 1833, p. 560. Frustulia Ulna Ilarv., in ]Manual, p. 204. 

 P P 



