FRESH-WATER DIATOMS FROM ICELAND 61 



Forma anormalis, cnfr. A. S. All., Tab. CCLXVII, figs. 3740, which 

 figures F. Fricke thinks can be understood thus: fig. 37, "vielleicht Auxo- 

 spore"; figs. 38 39, "vielleichl teratologische Auxosporen" ; fig. 40, "viel- 

 leicht die Zelle zweiter oder folgender Generation". 



10 samples (S.I, S.W. 3, E. 6). In these samples varying in dif- 

 ferent ways. 



Diatoma de Candolle 1805. V. H. Trt. 348. 



*Diatoma hiemale (Lyngbye) Heib. V. H. Trt. 350. A. S. Atl., 

 Tab. CCLXVII, figs. 1633 (Dial. hiem. mesodon). 



258 samples (S. 57, S.W. 64, N.W. 11, N. 33, E. 91, s. 1. 2). Hot 

 springs: 10. 



Area : Eur., As., Am., Grl. 



The reason, why I place this form as a Dial, hiemale, and in ad- 

 dition cite figures of D. hiemale, is, that I consider Heiberg (Consp. D. 

 58) is right when he says ''it is perfectly clear that it (o : var. mesodon) 

 is only a short form of Diatoma hiemale", and that ''specimens of both 

 forms are by Lyngbye determined as Fragilaria (now Diatoma) hiemale". 

 It is especially the short form met with in Icelandic material. 



Diatoma elongatum Ag. V. H. Trt. 349, Tab. XI, fig. 467. 

 Ulfjolsvatn (S.) A. F., Reykjavik (S.W.) H. Js., HallormstaSr (E.) B. P. 

 Area: Eur., Af., As., Am., Grl. 



Var. minus Grun. A. S. Atl., Tab. CCLXVIII, figs. 60 61. 

 Krossa (S.) H. Js., Stykkisholmur (S.W) H. Js. 

 Area: Eur., Am. 



Var. tenue Ag. V. H. Trait. 349, Tab. XI, fig. 468. 



35 samples (S. 10, S.W. 15, N.W. 1, N. 2, E. 6, s. 1. 1). Hot spring: 1. 



Area: Eur., Am., Spb., Fz. J. 



*Diatoma vulgare Bory. V. H. Trt. 348, Tab. XI, fig. 465. 



43 samples (S. 12, S.W. 12, N.W. 2, N. 7, E. 10). 

 Area: Eur., Af., As., Am., Grl., Fz. J. 



Denticula Ktz. 1844. V. H. Trt. 351. 



*Denticula elegans Ktz. V. H. Trt. 351, Tab. XXXI, fig. 860. 

 10 samples (S.I, S.W. 3, N. 5, E.I). Hot spring: 1 

 Area : Eur., Am. 



Denticula islandica sp. nov., Tab. nost. V, fig. 83. 

 Long: 40 //, lat: 4 //, costis 6,25 in 10 //. 



Valva lineari , apicibus subacutis. Costis seriebus punctorum 

 subtilissimorum interpositis. 



Vallanes (E.) B. P. 



Possibly this form is nearest related to Dent, subtilis Grun. (V. H. 

 Syn., Tab. XLIX, figs. 10 13), although it differs from this, especially in 



