436 Multiplication of Generic Synonymes. 



only in the membrane, which is found near the hook sup- 

 porting the anterior muscles ; so that many naturalists, to the 

 present day, persist in classing it with the genus Mytilus. 

 This appears to be the opinion of M. Deshayes, from the 

 notes which he has inserted in the new edition of Lamarck's 

 Histoire des Animaux sans Vertebres. 



M. Van Beneden of Louvain first made it the object of 

 attentive study ; and thinking that he had discovered in the 

 disposition of the mantle and of the nervous system marks 

 sufficiently characteristic, he made it the representative of a 

 new genus, called by him Dreissena. To this same genus 

 he refers some other species, particularly that which he has 

 lately described in the bulletin of the Brussels Academy, 

 under the name of Dreissena cyanea. M. Partsch of Vienna, 

 almost at the same time, described, under the name of 

 Congeria, a genus of fossil shells in the environs of the Lake 

 of Platen, and referred to this same genus shells which were 

 quite analogous with the Mytilus polymorphus. 



M. Rossmaller, another German conchologist, positively 

 created a new genus for the Mytilus polymorphus, and called 

 it Tichogonia Chemnitzii. This denomination has been 

 adopted by his countrymen, and we have in Wiegmann's 

 Archives d' Historic Naturelle, No. 1. 1837, some anatomi- 

 cal researches of M. A. Muller, who, in contradiction to the 

 observations of M. Van Beneden, pretends that the nervous 

 system of this mollusc is quite analogous to that of the 

 A'nodon. 



In this same Journal, M. Wiegmann has given, from some 

 specimens in the Berlin museum, a description of 5 species of 

 Tichogonia : — 



1. Tichogonia bilocularis (Mytilus bilocularis of Lamarck); 

 2. T. excisa, a new species brought from the Indian Ocean 

 by M. Lamarc-Piquot ; 3. T. virgata, a new species from 

 the South Sea; 4. Chemnitzii, which is the Mytilus poly- 

 morphus of Pallas; T. africana, which is the Dreissena 

 africana of M. Van Beneden. 



Finally, a very short time since, (in the month of March 

 last) M. Cantraine read to the Brussels Academy, a memoir, 

 in which he combats the opinion of his countryman M. Van 

 Beneden, contending that he only repeats what Pallas had 

 said ; and on his side, having adopted as a constant character- 

 istic the fortuitous existence of many membranes in the 

 Mytilus polymorphus, he thinks himself sufficiently authorised 

 to form from it a new genus under the name of Mytilina. 



M. Van Beneden in the scientific meeting of the 8th of 

 April, has replied to his attacks by maintaining the accuracy 

 of his observations, and his specific determinations. 



