54 THE VOYAGE OF H.M.S. CHALLENGER. 



These remained united, however, by a small triangular cushion at the superior extremity 

 of the two recently formed valves. 



This same Diatom was also found among the collections made at Tilanshang, one of 

 the Nicobar Islands, by the Austrian scientific frigate " No vara," and was named by A. 

 Grunow Asterionella frauenfeldii ; ' but, with this exception, no other naturalist has 

 recorded its occurrence, although it is found in almost all seas. 



Although at first sight this curious Diatom recalls the genus Asterionella, it is to be 

 remarked that in the latter the inferior extremities of the frustules are dilated and are in 

 contact with one another instead of adhering by means of small cushions. 



In the Synopsis des Diatomees de Belgique, by van Heurck and Grunow, which 

 has recently appeared, and in the section of Pseudoraphidiese (plate xxxvii.) the forms 

 which Grunow named Asterionella frauenfeldii are referred to the new genus 

 Thalassiothrix, to which there is also ascribed the very singular Synedra thalassiothrix 

 of Cleve. But, after a careful comparison of these two forms, they cannot be regarded as 

 congeners, the one — Asterionella frauenfeldii — having its frustules united by small 

 membranous cushions, while the other — Synedra thalassiothrix — is solitary or disposed in 

 parallel bands. 



With regard to the genus Thalassiothrix, Grunow says that it embraces some species 

 resembling Asterionella, but having on the margins spines or elevated points between 

 which one sees a short marginal striation. The structure here described is indeed pre- 

 cisely that of the Synedra thalassiothrix of Cleve ; but it cannot in any way be compared 

 to that of Asterionella frauenfeldii, the bacillar Diatom in which there is only to be 

 discovered a line of very salient marginal granules, which render the two small apices 

 indistinct. Hence it would be better, at least for the present, to exclude Cleve's Synedra 

 thalassiothrix from the genus Thalassiothrix altogether. 



But the Thalassiothrix (Asterionella) frauenfeldii of Grunow may, on the other hand, 

 be retained in that genus, although the generic definition must be somewhat modified. It 

 may be amended as follows : — Frustulis linearibus radiatim per pulvinulum gelineum 

 armilliforme unitis, bino erectiorum punctulorum ordine instructis ; post frustulorum 

 deduplicatione armilla disrumpitur, et frustula in seriem alternam per isthmum triangu- 

 larem cohalescunt. 



Thalassiothrix frauenfeldii (Grim.), Cstr. (Plate XIV. figs. 7 and 8.) 



Frustulis radiatim conjunctis, hinc in catenas alternas dispositis ; a latere zonali 



anguste linearis, valvis arctissime linearibus, utroque margine serie unica punctulorum 



(spinularum ?) evidentium ornatis. Ad insulas Nicobar, ad Java, in mari Sinensi et 



Japonico, in Adriatico, in Tyreno et alibi. 



1 Verhandl. d. L Jc. zool.-hot. Gesellsch. in Wien, 1S63, p. 140, pi. xiv, — Diatoinaceen der JNovara-Expedition 

 —fig. 18. 



