174 CKYPTOGAMIA. 



DIATOM ACE M, 



AND OTHER MICROSCOPIC FORMS. 



The species of Diatomacece, &c, included in the following list, were 

 detected adhering to the dried specimens of Algae collected in the 

 Expedition. Among them, are a number of interesting forms which 

 are believed to be new. These are indicated in the catalogue, by an 

 asterisk prefixed to the name. 



PUQET SOUND, NORTHWEST AMERICA. 



* Amphiteteas Wilkesii, Bail. & Earv. (Tab. 9, fig. 1, 2.) 



A. loricis prismatico-talmlaribus, lateribus concavis, primaria longitudi- 

 naliter striato-punctata medio transversim zo?iata, secundaria guadran- 

 gula angiitis productis rotundatis, superficie cellulis minutis in lineas 

 simplices furcatasque dispositis notata, promineniiis jugalibus punc- 

 tulatis. 



This beautiful species is nearly twice as large as English specimens 

 of Amphitetras antediluviana, Ehr., from which it is also distinguished, 

 by its tubular form, and by the arrangement of the cells. Its sides 

 are deeply concave, the angles produced and rounded. The surface 

 is covered with small cells, disposed in simple and forked lines pro- 

 ceeding from the centre of the discs. The specimens were found 

 adhering to the base of Costaria Turneri, and other Algce. 



* Arachnodiscus Ehrenbergii, Bail. (Tab. 9, fig. 9, 10.) 



A. disci granulis gemmaceis majoribus (in ¥ y" 10-12) in seriebus concen- 

 tricis ; cellulis concentricis nullis; radiis 20-31 cequalibus, interjectis 

 swpe brevioribus. Diani., ^'" 



The first published account of a species of this genus, was given by 

 Ehrenberg, in the Berlin Monatsbericht, 1848, p. 7, where he found 



