20 BRITISH DIATOMACEjE. 



as that author gives Echinella ohtusa of Lyng. Tent. Ixix. F., and Frustvlia 

 obtusa of Ag. Consp. p. 44, as synonyms of his species. Dr. Greville's 

 Herbarium, containing original specimens of Lyngbye's and Agardh's species, 

 which are identical, enables me to state that that species is different from the 

 present, and in fact belongs to the genus Diatoma, the zigzag arrangement of 

 the frustules being perfectly distinct, and the side view of the valve being 

 slightly constricted near the extremities and inflated in the middle, precisely 

 as may be seen in occasional specimens of Diatoma elongatum. If entitled to 

 rank as distinct, Lyngbye's specimen must be placed near that species, and 

 take the name of Diatoma obtusum. Ktitzing's figure of Denticula obtusa 

 accords so nearly with the present, that I am disposed to think that he had 

 our species before him, and must leave the reference to stand with a mark of 

 doubt until the examination of an actual specimen enables me to determine 

 the point. If the figure given by Rabenhorst be original, it would confirm the 

 view here given, as it accords exactly with my species, and not at all with 

 Frustulia obtusa, Ag., which is given as its synonym. 



Plate XXXIV. 292. 



2. Denticula tenuis, Kutz. Frustules linear, truncate ; V. lanceo- 

 late, acute; stria? 40 in *00l"; costae about 12 in , 00l". Length 

 of frustule -0006" to -0015". v.v. 



Kutz. Bacill. xvii. 8 1 Denticula acuta, Raben. Siissw. Diat. i. 7 ? 



Fresh water. Plumpton, Sussex, April 1852. Lame, July 1853, W. Sm. 

 Lancaster, Nov. 1853, Mr. Johnson. Mountains, Forfarshire, Dr. Dickie. 

 Isle of Arran, Dr. Arnott. (Fountain at Nismes, May 1854, W. Sm.) 



A small and more acute form than the last, but doubtfully distinct. 



Plate XXXIV. 293. 



3. Denticula inflata, n. sp. Frustules linear, or elliptical ; V. oval, 

 with rounded, or acute extremities; striae 40 in *00l"; costae 

 about 12 in -001". Length of frustule -0005" to -0007". v.v. 



Fresh water. Beachey Head, Sussex, Aug. 1852, W. Sm. (Chateau d'Eau, 

 Montpellier, and Fountain at Nismes, May 1854, W. Sm.) 



The smaller size and broader valve alone distinguish this species from the 

 last two, with which it may be necessary eventually to unite it. 



Plate XXXIV. 294. 



4. Denticula ocellata, n. sp. Frustule linear, truncate, with con- 

 spicuous foramina on F. V. ; valve linear, elliptical ; striae 40 in 

 •001" ; costae 10 in -001". Length of frustule -0008" to -001 1". v.s. 



Fresh water. Near St. Abb's Head, July 1855, Dr. Balfour. 



