400 M. Ehrenberg on (he Living Representatives of the 



N. carinata. We likewise distinguish a form very nearly re- 

 lated to Fragillaria diophthalma, and great numbers of another 

 almost identical with Gomphonema gracile. Of the eight 

 forms which have been recognised, four evidently belong to 

 those of fresh water and the present era. They are not smooth 

 on the surface, full in the interior, resembling stony micro- 

 scopical nuclei, just as we often find in shells, but very rarely 

 among the Infusoria. 



The author has placed before the Society drawings of the 

 American forms and those of Geistinger- Wald, as well as spe- 

 cimens of polirschiefer sent to him by M. Steininger. 



Diagnosis of New American forms. 



Podosira, new genus. 



Character of the genus : animal belonging to the family of the Bacil- 

 larii possessing the characters of Gallionella, but supported by a pe- 

 dicel. 



P. moniliformis, Trochiscia moniliformis Montagne 1837, corpuscles 

 globose, separate, very finely punctate; the ovaries vesicular, green- 

 ish. Du Petit Thouars found it at Callao on the Callithamnius 

 floccosus and Polysiphonia dendroidea, and it was first detected 

 by Montagne on specimens of these transmitted to him. 

 Grammatophora, new genus. 

 Character of the genus : animal belonging to the family of the Bacil- 

 larii, possessing the external characters of Tabellaria, but divided 

 into three longitudinal-: compartments by two internal folds often 

 curved in various directions. 



G. oceanica ; bacilli quadrate or oblong ; the middle laterally turgid ; 

 gradually attenuated at both ends, and obtuse ; the ovary trilobed 

 on both sides and green. Gathered alive along with the former 

 by Du Petit Thouars on the algse of the Peruvian seas at Callao. 

 G. Mexicana, bacilli quadrate, or oblong ; the centre equal on the 

 sides ; both ends suddenly decreasing and obtuse. Found in a 

 living state by Charles Ehrenberg on the algse of the Mexican 

 ocean at Vera Cruz. 

 G. undulata, bacilli quadrate or oblong ; laterally moniliform, un- 

 dulated, four times constricted, hence five-jointed ; the apices 

 obtuse. Found alive by C. Ehrenberg in the same place as the 

 preceding. 

 The fossil species which is found in the cretaceous deposits at Oran, in 

 Africa, and formerly named Navicula Africana, now G. Africana, 

 differs in the following characters : bacilli oblong, scarcely turgid in 

 the middle, and very obtuse at the apex. It is now very likely that 

 JVuvkula Bacillum should be referred to the genus Tabularia. 



