414 ALGiE DIATOMACEiE. [Cymbella. 



separating. Ag. Syst. Alg. p. 10, et Conspect. Crit. Diat. p. 18* 

 Grev. Crypt. Fl. t. 298.— Ulvafcetida, E. Bot.t. 2101. 



On rocks, stones and various small Algce, in the sea. Salt-marshes, 

 "Norfolk, Dr. Hooker. Ireland, Miss Hulchins. Appin, Captain Car- 

 michael. — Tufts one to three inches in length, of a pale reddish, yellow- 

 ish or greenish colour. Filaments destitute of an external membrane, 

 exceedingly tender and gelatinous, varying in thickness according to the 

 number of smaller filaments which are united together, each of which is 

 marked by a single series of frustula. 



10. S. prostration, Grev. (procumbent Schizonema); "threads 

 brown procumbent simple flexuose obtuse containing a single 

 row of granules which are either simple subelliptic with one 

 margin more curved, or cylindrical with obtuse ends, or double 

 of two cylindrical portions." — Momma prostratum, Berk. Brit. 

 Aly. p. 15. t. 4./ 3. 



On the boards of a sluice, forming a very thin brown mucous stratum, 

 Rev. M. J. Berkeley. — This is a very curious plant, known to me 

 only by my friend Mr. Berkeley's description and representation, which 

 I can depend upon as perfectly correct. If it really belong to the pre- 

 sent genus, it is a specimen of its most elementary form. It is well 

 remarked by Mr. Berkeley, that the frustules, taken apart from the fila- 

 ments, would belong to Frustidia, and nearly resemble F. obtusa. 



112. Cymbella. Ag. Cymbella. 



Frustula elliptical, binate, free, or imbedded in a mucous 

 mass. — Name ; the diminutive of cymba, a boat ; in allusion to 

 the form of the frustules, particularly in one species. 



1. C. hyalina, Ag. (pellucid Cymbella); frustula simple hya- 

 line lanceolate and acute at each extremity. — Ag. Conspect. 

 Crit. Diat. p. 7. 



Shallow ditches. Near Edinburgh, Dr. Greville. Early spring. — 

 Floating on the surface, or after the evaporation of water, forming a 

 pulverulent stratum. Colour a yellowish or olivaceous-green. The 

 frustula are excessively minute. 



2. C. minor, Ag. (lesser Cymbella); frustula simple lanceolate 

 and acute at each extremity with a narrow band, the ends some- 

 what opaque. Ag. Conspect. Crit. Diat. p. 8. — Frustulia minor, 

 Ag. Syst. Alg. p. 2. — F. lanceolata, Berk. Brit. Alg. p. 13. t. 4. 



f- 1 - 



In pools and quiet streams, Rev. M. J. Berkeley. — Plant forming a 

 soft spongy yellowish-brown mucous stratum, entirely composed of 

 frustula. Frustula very pale yellow, with a central transverse hyaline 

 band, which, however, is sometimes wanting. The description of Mr. 

 Berkeley's plant comes so near to that of C. minor, that I am induced 

 to consider it as the same. Mr. Berkeley has indeed himself remarked 

 its resemblance. The C. lanceolata of Agardh is a different species. 



3. C cymbiformis, Ag. (Corricle Cymbella); frustula binate 

 cymbiform obtuse somewhat curved hyaline with a dorsal and 

 central yellow globule. Ag. Conspect. Crit. Diat. p. 10. 



