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



Asterionella, Hassall. 



The genus Asterionella, instituted by Hassall in 1855, is characterised by the following 

 features : (l) Its frustules are grouped in a stellate manner, and (2) when viewed in profile 

 they are constantly inflated at the base, and sometimes also at their superior extremities. 



Up to the present time all the species included in this genus have been freshwater 

 forms, with the exception of the Asterionella bleakeleyii of W. Smith and the Asterionella 

 frauenfeldii of Grunow, the latter of which was afterwards ascribed to the genus 

 Thalassiothrix. Among the collections procured by the Challenger, however, two different 

 types, which were gathered on the surface of the Antarctic Ocean near the ice-barrier of the 

 South Pole, must be ascribed to the Aster ionelloe, but it is to be borne in mind that, as 

 numerous frustules of Eunotia arcus, "W. Sm., 1 were found in the same collection, it is 

 unquestionable that in many cases terrestrial Diatoms which vegetate on the glaciers of 

 the Antarctic, and which represent the last traces of the icebergs that have been melted 

 by coming into contact with warmer water, float upon the surface of the waters in these 

 localities. Moreover, since it has been clearly proved that the other species of the genus 

 Eunotia do not vegetate except at an elevation of several hundred feet above the level 

 of the sea, it is manifest that it is impossible here to decide whether the Asterionella, 

 which have now to be recorded, should be regarded as terrestrial forms, or whether they 

 must be viewed as being strictly marine. 



Although these new forms cannot be identified with Asterionella bleakeleyii of W. 

 Smith, which was till recently the only marine species that had been observed, it may here 

 be remarked that I have observed other marine Asterionella; at the island of Lesina in 

 Dalmatia — a region which is exceedingly favourable for research in this department of 

 marine biology. In this locality, by means of small nets, there was found on the surface of 

 the sea, and floating among many other organic forms, an Asterionella which could be 

 readily distinguished by the linear form of the frustules ; these were at the same time 

 provided with a swelling at the inferior extremity, and were radiately disposed so as to 

 present a stellate appearance. This form, too, was remarkable from the fact that the series 

 did not form a solitary star with only a few radii, but presented, on the contrary, a long 

 chain of very numerous frustules, which were disposed in such a manner as to form several 

 spiral turns, so that the name Asterionella spiralis, which has been applied to the species, 

 is exceedingly characteristic. 



Asterionella glacialis, n. sp. (Plate XIV. fig. 1.) 



Frustula a basi inflata exiliter linearia ; valvis inferius rotundato-inflatis, et binis 

 lineolis notatis. In mari Antarctico. 



1 Synopsis of the British Diatomacese, vol. i. p. 15, pL ii. fig. 15. This Diatom is equivalent to Navicula 

 arcus, Ehrenb., Inf., pi. xxi. fig. 10, Cymbella (?) arcus, Hass., Alg., C. 6, and to Ceratoneis arcus, Kg., Baa, pi. vi. 

 fig. 10. 



