362 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



GYROSIGMA Hass. 



Gyrosigma ITasP. Hist. Brit. Algae 1: 485. pi 102. f. 11. 18J5. Rabh. Sus^w. Diat. 



.47. 1853. Clcve, char, emend. Sv. Vet. Akad. Ilandl. 26': 112. ISQl. 

 rlenrodijma W. Sinilli, Ann. Maj^:. Xat. Hist. 1. pi 1-2. 1852. Syiiop. Brit. Diat. 



1: GI. p/.if^-^f. 1853, Rabh. Kb Eur. A1-. 1: 230. 18G4. Prildi. Hist. Tnfiis. ed. 



4. iHo. bS(U. Gniih Verb. Zoub Rob (ies, ^Vien 10: 555. 18Glb Cleve & Grnn. 



Sv. Vet. Akad. Haiidb 17-: 48. ISSO. Van lleur. Syno]). 114. pi 18-2U 1881; 



Treat. Dial. "249. pi 6 7, 28. 1890. Rerag. Le Diatoniiste 1^"': 1-35. pi 1 10, 



1891. Castr. Rep. Voy. (^halb Rot. 2: M\. 1880. Griff, ct IleiiL Micr. Diet. ed. 



4. GOG. pi 15, 1883. Dc Toni. Sylb Alg. 2: 231. 1891. Cleve, Sv. Vet. Akad. 



Handb 26~: 112. 1894. 

 Frusiidia C. Ag. in part; KuLz. Linnaea 8: 555 (nos. 49-50). pi 14- f* 35-36. 1833. 

 Navicvhi Rory, in part; Ehrenb. Iiifus. 180 181 (nu«. 226-230). pi 13. / 10-14^ 



1838. Kiitz. Raeilb 102 (no. 132). pi 4.f. 32. 1844. 

 Toxonidca Donk. Trans. Mier. Soe. Loud. n. s. 6: 19. pi 4,f. 1-2. 1858. Cleve, Sv, 



Veb Akad. Handb 26': 45. 1894. Van Heur. Treat. Dial. 247. 1896. Rritch. 



Ilirtt. Infus. ed. 4. 920. ISGl. Rerag. be Diatomiste l-*-"^: 27. pi 'J. 1891. 

 Donkinla Ralfs inPriteb. Ili.st. Infus. ed. 4. 92(1. pi S.f. VJ. 1861. Van Heur. Treat. 



Diat. 248. 189G. Terai;. Re Diatoniiste 1^ ■': 29. pi IL 1891. 

 Rhommywa Grnn. Hedwi.^da 6: 10. 18G7. Van Heur. Treat. Diat. 260. 1896. 



Rerag. Le Diatomi^tt^ l"*'"': 30. pi 9-10. 



This genus of diatoms is one of the best delined and most yhiirply separated of the 

 - large genera. Its valves are more or less sigmoid, both as to their outline and in respect 

 to the trend of the raphe, Tliey are e\ eiily marked with delieate slriations of great 

 beauty and often of extrenu^ delieaey, either in two directions, transverse and longi- 

 tudinal, or in three <lireetions, one transverse ami two obliciue, the three being at 

 angles approximately of 60° to each other. This striation covers the entire valve 

 with a gauzy network, except a very narrow longitudinal space through which runs 

 the raphe and a minute area around tbe central nodule. Jbe valves are as a 

 rub' convex, thin, made up of two or three layers, and tberefore strongly prismatic. 

 The zonal view is in most cases extremely narrow compared to tbe valval view. Their 

 beauty, wide distribution, ami importance as tests of the elliciency of microscope 

 objectives have resulted in their being juore generally known and carefully studied 



than most other genera, 



WiUiam Smith's generic name, Rleurosigma, is very api)ro])riate and has been uni- 

 versally accepted in i)reference to the earlier one of Hassalb Rut there can be no 

 question of the validity of Gyrosigma. We find it in his Rritish Algae as a niono- 

 typic genus, based on (/. hippocampn (Rbrenb.) ITass., the description and illustration 

 of which arc unmistakable, Ilassall also (piotos Ebrenljerg's excellent reference to 

 this diatom, « as Naviada hippocampus Ehrenb. The reasons advanced by Rrebisson, 

 Ralfs, and i>thers, for preferring Smith's name are wholly ina<lequato; and although 

 we are indebted to Smith for a most clear and comprehensive analysis of this genus 

 it is necessary to recognize the right of Ilassalbs name to represent these diatoms. 



Several attempts have been made to create new genera out of certain species of 

 Gyrosigma having more or less striking i>eeuliarities. The lirst was the separation 

 of all species having an an-nate instead of sigmoid raphe, with valves extremely con- 

 vex on one side and nearly straight on llie other (i. e., strongly asymmetrical on their 

 longitudinal axis). These were placed in a genus, Toxonidia, by Donkin.'^ Tbe 

 next separation was by Ibdfs of valves wiili <»xlreniely sigmoid raphe, the ridge of the 

 raphe being raised into a keel above the rest of the valve, except at the central nodule. 



I' Ehrenb. Iiifns. ISO. pi. 13. f. 11. 1S;;S. 



bDonk. Trans. Micr. Soe. Loud. n. p. 6: 10. pi. S.f.l. 1858. Mocb. Diat.-taf. pi. 18, 



f. 1. 1890. 



