428 Linnean Society. [June 5, 



June 5. 



Thomas Bell, Esq., President, in the Chair. 



Mr. "Ward, F.L.S., exhibited specimens in flower of Gentiana verna 

 from Galway, and Cerastiuni latifolium and Draba frigida, from the 

 Dovra Range of mountains in Norway, all of which have flourished 

 freely on some peaty banks in liis garden at Clapham for the last 

 three years. Mr. Ward also exhibited collections of dried speci- 

 mens of Alpine plants from Switzerland and Norway. 



Mr. Stevens, F.L.S., exhibited a splendid new Butterfly {Orni- 

 thoptera Brookeana, Wallace), collected by Mr. Wallace in Borneo. 



Read the first of a Series of Memoirs, entitled " Horse Carcino- 

 logicse, or Notices of Crustacea. I. A Monograph of the Leuco- 

 siadce, with observations on the relations, structure, habits and dis- 

 tribution of the family, a revision of the generic characters, and 

 descriptions of new genera and species." By Thomas Bell, Esq., 

 V.P.R.S., Pres. L.S. 



The author commences this paper with remarks on the distinct 

 limitation of the Leucosiadee, and the absence of any obvious osculant 

 forms by which to associate them closely with neighbouring groups 

 of the Oxystomata, and the no less striking want of any distinct re- 

 presentation of this family within the limits of other members of 

 the same great group. He refers, however, to a probable affinity in 

 the structure of the type of the PinnotheridcE, which has hitherto 

 been overlooked. The apparent approximation of the genus Oreo- 

 phorus to the Calappadce is also suggested, and a corresponding 

 tendency to a lateral expansion of the carapace pointed out in the 

 genera Lithadia, Nursia, Phlyxia and Ebalia. 



The history of the progressive knowledge of the family from its 

 first detection by Fabricius as a distinct group is then given. The 

 author enters at some length into the consideration of the nature of 

 specific characters in general, and the necessity of adopting such as 

 are tangible and certain ; and after deprecating the use of such as are 

 merely comparative between diff'erent species, he urges the import- 

 ance of giving, in all cases when a new species is described, such a 

 definition as shall point out as briefly as may consist with clearness 



