BRITISH DIATOMACE^E. 97 



strife 45 in -001". Length of valve -0032" to -0044". Breadth of 

 valve -0006" to -0007". v. v. 



Gyrosigma transversale, Micrographic Dictionary, May 1854, pi. xi. 37, 38. 

 Pleurosigma Naviculaceum, Breb. Diat. Cherb. fig. /. 



Marine. Stomach of Pecten, Coast of Sussex, February 1853 and March 

 1854; Kinsale Harbour, April 1855, &c, W. Sm. Stomach of Mytilus, 

 Coast of Devonshire, Mr. D Alguen, March 1854 ; Plymouth, January 1854, 

 Dr. Arnott. Thames mud, March 1854, Mr. Roper. Milford Haven, April 

 1854, Mr. Okeden. Lyme Regis, Dorsetshire, 8 fathoms, November 1855, 

 Mr. Capron. 



The present species affects deep water, and seems plentifully diffused along 

 the British coasts. Its outline is that of a Navicula ; but no one familiar with 

 these oi'ganisms will hesitate to place it with the sigmoid forms of the Pleuro- 

 sigmata, to which the position of its median line and the structure of its valve 

 manifestly ally it. 



The alliterative blunder in the name Gyrosigma must be my excuse for not 

 adopting it as the designation of this division of the Naviculacece, an excuse 

 whose validity I find thus admitted by M. De Brebisson in the brochure above 

 quoted : — " Gyrosigma, Hassall. Peut-etre ce dernier nom de genre n'etait-il 

 pas bien convenable selon les lois de la nomenclature ; dans tous les cas, il est 

 certain que, malgre son droit de priorite, il est a peu pres generalement aban- 

 donne, comme cela arrive promptement pour les puissances dechues. D'ailleurs, 

 on est d'autant moins dispose a reprocher ce changement de nom a M. W. 

 Smith, que le soin tout monographique qu'il a apporte a 1' etude des nom- 

 breuses especes de Pleurosigma qu'il a decouvertes, en fait un genre tout 

 a lui." 



59. Synedra undulata, Bail. F. V. linear- truncate, arcuate ; V. 

 linear-arcuate, inflated at the centre and towards the rounded 

 extremities ; margins undulated ; nodule obsolete ; striae monili- 

 form, 24 in -001". Length of F. -0134" to -0166". Breadth of V. 

 at centre *00033" ; at extremities *00025" ; at the intermediate 

 points -00017". v.v. 



Bail. MSS. et specim. Synedra undulans, Greg. Mic. Journ. vol. 3. pi. iv. 23. 

 Toxarium undulatum, Bail. Mic. Organ, figs. 24, 25. 



Marine. Cork Harbour : attached to Polysiphonia nigrescens, dredged in 

 depth of 5 fathoms, July and October 1855, W. Sm. Near Lyme Regis, 

 Dorsetshire, in 8 fathoms, November 1855, Mr. Capron. 



This beautiful and curious species was first determined as British by Dr. 

 Gregory, who found portions of its valves in a sandy deposit from the valley 

 of Glenshira near Inverary, and subsequently a single fragment of a valve in a 

 gathering I made in Poole Bay in 1849. The specimens I afterwards col- 



VOL. II. II 



