202 ON THE NAIADES, 



After examining numerous specimens in Europe of the littoralis, I 

 have strong doubts if the shell described by me in a former memoir, 

 under the name of incurvus, be not a peculiar variety of it. It cer- 

 tainly has a marked similarity to a fine transverse specimen of littoralis. 

 The specimen from which my description vs^as made, was sent to me 

 as a " non descript from Gibraltar," by Mrs Ma we. I had not at that 

 time seen very fine specimens of the littoralis, and it did not strike me 

 that there was a similarity to such as I had. While in London, that 

 excellent conchologist, Mr G. B. Sowerby, showed me a specimen 

 precisely similar to mine, and which I think he informed me was from 

 the collection of the veteran Humphreys. In one valve was marked 

 in ink "Brazil;" in the other the name of the person who is supposed 

 to have brought it from that country. 



Unio semirugata. The specimen which I examined in the Duke 

 de Rivoli's cabinet, is the one mentioned as being in Lamarck's own 

 cabinet. It is a young littoralis, with rather more undulations than 

 usual. 



Unio nana. I saw this species only in the collection of Baron de 

 Ferussac. All the specimens were old and depauperated, and their 

 similarity to littoralis so great, as to induce me to believe that when 

 better individuals are procured, they will easily be referred to that 

 species. 



Unio ilelodonta. The specimen cited, and which I examined in the 

 cabinet of the Duke de Rivoli, I suspect to be the lacteolus (nobis). 

 It has the beaks eroded, and therefore does not present the peculiar 

 character of radiating folds at the point of the beaks, which is conse- 

 quently omitted in Lamarck's description. 



Unio sulciilens. In the Duke de Rivoli's collection — it is a com- 

 pressed complanatus (Soland.), from the Connecticut River, where 

 this species is more disposed to assume that character than in any 

 river in the United States with which I am acquainted. 



Unio rostrata. This is one of the numerous species made from the 

 pictoriim of authors. It is merely an elongated variety of that species 

 in all the cabinets where I have seen it in Europe. 



Unio Batava. This is a distinct species from pictorum. Baron de 

 Ferussac thinks that Maton and Racket are entitled to the species. 



