Prof. G. J. Allman on a new genus of Molliisca. 3 



blished genera, and I accordingly noticed it at the York Meeting 

 of the British Association in Sept. 1844, under the name of Al- 

 deria amphibia^ an appellation under which it has been also re- 

 corded by Mr. Thompson in his Report on the Invertebrate 

 Fauna of Ireland, and by Messrs. Alder and Hancock in their 

 Report on the British Nudibranchiate Mollusca. 



Shortly after my noticing the little animal in question as a 

 new genus of Mollusca, I received a letter from Mr. Alder, ac- 

 companying an extract from a paper by Dr. Loven of Stockholm, 

 which had just appeared in a foreign periodical, and which con- 

 tains an account of a Nudibranchiate mollusk referred by Loven 

 to the genus Slili(j/er, Ehrenberg, and described by the Swedish 

 naturalist under the name of S. modestus. 



On comparing Loven's description of S. modestus with the sub- 

 ject of the present communication, it was evident that Loven' s 

 animal and the Nudibranch of the Irish salt-marsh were the 

 same. A reference however to the characters of Ehrenberg's 

 genus StiligeTj rendered it by no means so apparent that Loven 

 was correct in the generic location of his mollusk. 



Under this difficulty Mr. Alder received a letter from Dr. Loven, 

 in which is the following passage respecting S. modestus : — 



^' A very r^re animal. It is now ten years since I found my 

 two specimens, one of which was lost by accidojttt. Fortunately 

 I described and figured it alive, for I never nift with any more. 

 Stiliger, Ehren., has only one species, and as it requires but little 

 to widen its characters enough to let in my new species, I thought 

 it advisable to do so, and still tlyjik I was right in so doing. ' At 

 least I have not a superfluous genus on my conscience. Nothing 

 is more easy than to npke new genera, but the question is to 

 find out the true generic' characters, which, particularly in the 

 Nudibranchia, is rather difficult.^' 



On the above passage, Mr. Alder in a letter to me remarks : 

 ^' So far Dr. Loven ; and after his opinion, you will perhaps 

 scarcely venture to institute your new genus, though Mr. Han- 

 cock and I, after mature considemtion, think you wouM Jse right 

 in doing so.^^ With the Englishr naturalists I agree, and ifty^'i- 

 ginal opinion 'with respect to the necessity of a new genus for m^^ 

 reception of the salt-marsh Nudibranch remains unaltered. The 

 characters indeed of this moUusk^pan scarcely be confounded with 

 those of Stiliger, and in order that tliis matter may be made more 

 apparent, I here subjoin Ehrenberg's characters of the last-men- 

 tioned genus from the ^ Symbolse Physicse.' 



" Stiliger, nov. gen. 

 '^ Gen. Char. Habitus Eolidia. Corpus oblongum, pallio dis- 

 crete nullo. Latera corporis branchiarum stiliformium seriebus 



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