BRITISH DTATOMACE^. 81 



10. Gomphonema Vibrio, Ehr. V. almost linear, very slightly at- 

 tenuated, obtuse ; striae 22 in -001". Length -0021" to -0031". v.v. 



Ehr. in Kiitz. Bacill. xxix. 75. 



Fresh water. Wray near Lancaster, M)\ G. Smith, Aug. 1851. Lough 

 Mourne and Peterhead Deposits. Marl, Co. Down. 



Plate XXVI XL 242. 



11. Gomphonema? curvatum, Kiitz. Stipes elongated, filamentous 

 and dichotomous ; F. V. curved ; V. enlarged towards the upper 

 extremity, which is rounded and inflected, attenuated towards the 

 lower, which is acute ; nodules absent in the convex (outer) valve ; 

 striae 30 in -001". Length -0007" to -0021". v.v. 



/3. Striae more distinct, 22 in •001". 



Kiitz. Bacill. viii. 1. Goinp. tninutissiminn, Ehr. Lif. xviii. 5. Ralfs, Ann. 

 vol. xii. pi. xviii. 9. Hass. Alg. c. 3. Li Conj. Thw. Ann. vol. xx. 

 pi. xxii. fig. B. Prit. Anim. xiv. 9, 10, 11, 12 & 17. 



Fresh water : ponds, very common. Near Belfast, Aug. 1849 ; Plumpton, 

 Sussex, Apr. 1852, W. Sm. Pond, St. James's Park, Jan. 1852, Mr. Shad- 

 holt. Var. /3. Shoreham, Kent, Mr.Jenner, 1843. 



Plate XXIX. 245. 



12. Gomphonema ? marinum, J'F. <S^m. iStipes Incrassated, branching 

 in an irregular manner ; F. and V. as in the last species ; striae 35 

 in -001". Length -0005" to -0021". v.v. 



Gomp. curvatum, /3. marinum, Kiitz. Bacill. viii. 3. Prit. Anim. xvi. 11. 



Marine: frequent. Coast of Sussex, Oct. 1851, &c. In Conj. Mar. 1852, 

 W.Sm. 



Plate XXIX. 246. 



The last two species are characterized by several peculiarities. The curved 

 form of their frustules, and the want of symmetry in the valvular markings 

 are notable circumstances, which seem to place them apart, while the inflection 

 of the upper extremity of the valve, easily recognised upon a side \iew, is a 

 feature not found in any other species of Gomphonema. The last circumstance 

 would seem to point to Rhipidophora as their appropriate position ; but the 

 presence of a central nodule on the inner surface, and the more perfectly sili- 

 ceous nature of the valves, forbid their union with that genus. The species 

 are so closely alUed to each other, that it becomes difficult to distinguish them 

 by a verbal description, if we confine our attention merely to the frustules ; but 

 the general appearance of the growing plants, arising from the characters of 

 their stipes, is very different, and their habitats are so wide apart, that there 

 can be no doubt of their distinctness. 



