6274 



Crustacea. 



Notes on two Crustacea new to Britain. By J. R. Kinahan, M.D., 

 Secretary to the Dublin Natural-History Society. 



Platyarthrus HoFFMANSEGGii, Brandt. 



On the third of last month I received from my friend the Rev. A. R. 

 Hogan, a letter containing specimens of an Oniscoid, found by him in 

 ant-hills of Formica rufa and allied species, near Weymouth, and 

 which has been up to this time unnoticed in Britain, and but meagrely 

 described on the Continent. 



The curious companionship of Isopod Crustacea and Ants was, I 

 believe, noticed for the first time by M. H. Lucas, in the case of an 

 Oniscoid found by him at Medeah, in Algeria, in company with 

 Formica testaceo-pilosa, and which he has recorded under the name of 

 Porcellio myrmecophilus, in a paper in the ^ Revue et Magasin de 

 Zoologie,' p. 335, 1855, intituled Observations sur deux Nouveaux 

 Genres de Coleopteres (Oochrotus et Merophysia) qui vivent dans les 

 four milieres des Formica barbara et testaceo-pilosa." I may remark, 

 in passing, that a careful examination of type-specimens of this 

 species, kindly afforded me by the discoverer, has satisfied me that 

 it does not belong to Porcellio as restricted by Brandt ; and I have 

 therefore, with M. Lucas's permission, established a genus Lucasius 

 for it, and hope shortly to describe it more fully as Lucasius myrme- 

 cophilus, along with a number of new and undescribed genera of the 

 group. 



The Isopod sent me by Mr. Hogan proves to belong to the genus 

 Platyarthrus, established by Brandt in his * Conspectus Monographia 

 Oniscodorum,' and is probably identical with the species, P. Hoffman- 

 seggii, Br., there noted by name only (which is, I believe, identical 

 with Itea crassicornis, jKof/i.), as M.Lucas kindly gave me, when in 

 Paris, specimens identical with Mr. Hogan's, which he had obtained 

 in abundance in the ant-hills of Formica rufa, at Fontainbleau, near 

 Paris, and which is therefore most probably identical with the species 

 found by Brandt in Germany. 



The following descriptions have been drawn up from the speci- 

 mens : — 



Genus Platyarthrus, Brandt. 



Body flattened. Head transverse ; lateral and frontal lobes well 

 marked, arising from third ring. Internal antennae inconspicuous, 

 three -jointed. External antennae seven -jointed. Peduncle, — • 

 second joint lobed internally; fifth broad and flattened (whence 



