Microscopic Animals of the CJialk- Formation. 397 



In 1837,M. Camille Montagne of Paris described, in the An- 

 nates des Sciences Naturelles, a century of new cryptogamous 

 plants, and among these two microscopic forms accidentally 

 found on the marine confervas of Callao in Peru, one by M. 

 d'Orbigny, the other by M. du Petit Thouars ; he named the 

 one Achnanthes pachypus, the other Trochiscia moniliformis. 

 M. Montagne shewed the specimens of these two forms to M. 

 Ehrenberg when in Paris in 1838, and the latter considered 

 them to belong to the Bacillariees. He thought that the Tro- 

 chiscia rather belonged to the genus Meloseira Agardh (Gal- 

 lionella), and designated it by the name of moniliformis. 



At all events, these two forms are different from those of 

 Europe. The Achnanthes pachypus is a distinct species of 

 this genus, very nearly related to A. subsessilis. The form of 

 the Trochiscia or Meloseira is more remarkable. It possesses 

 a character which raises it to the rank of a particular genus, 

 and it is the first extra European genus which has been well 

 determined. Its form is that of a Gallionella with a pedicel 

 like the Achnanthes. It is to the Gallionella what Lynedra 

 is to Navicula, or what Podosphenia, Gomphonema, or Echi- 

 nella are to Meriodon, or rather Cocconema to Eunotia, Sten- 

 tor and Trichodina to Vorticella, and Epistylis or finally Eu- 

 glena to Colacium. In fact, it is necessary to unite all the 

 genera with a pedicel to those deprived of this organ which 

 approach them, if it be not thought that the characters of the 

 form of Peru are sufficient to constitute a new genus. But if 

 this distinction is made, this form, the first extra-European 

 one which shall have been definitively characterized, will take 

 the generic name of Podosira moniliformis. 



A more attentive examination of the small branch of Poly- 

 siphonia dendroidea on the alga of Callao to which the Podo- 

 sira was attached, has afforded facts of even greater interest 

 in a scientific point of view. We have there found two hitherto 

 unknown forms of Bacillariees. One of these has all the ap- 

 pearance of Tabellaria vulgaris (Bacillaria vulgaris), but it is 

 divided in the interior by two partitions or curved folds ac- 

 cording to the length of each distinct aciculus in their cham- 

 bers or cavities. This structure of distinct aciculi throws 

 some light over that of the same bodies in the chalk-marl of 



VOL. XXX. NO. LX. APRIL 1841. C C 



