410 Dr. Baird on some new Genera and Species 



habits* This little animal takes up its abode in any empty uni- 

 valve shell, which continues to form its habitation until its 

 increasing size renders it necessary for it to abandon it for a 

 larger. It often happens that it fixes upon one already tenanted 

 by another of its species, and a desperate struggle ensues, which 

 is rarely discontinued until either one or both be disabled. 



The few shells that are to be found on the beach in the Straits 

 are small and common, such as the Solen truncatus, or truncated 

 razor-sheath; the Mya nicoharica, or Nicobar trough -shell, or 

 gaper; the Venus decussata, or decussated Venus; the Murex 

 trihulus, or thorny woodcock ; the Murex rana^ or frog Murex ; 

 the Mytilus plicatus, or plaited muscle ; the Trochus indicus, or 

 Indian top ; and Valuta amis Midce, Midas^s ear volute. 



The entomology of the Straits presents a wide field for the 

 naturalist, but several circumstances prevented my turning my 

 attention to it. The few specimens that I had an opportunity of 

 noticing are as follows : — the Atlas moth ; the Papilio memnon, 

 or Memnon butterfly ; the Papilio pamnon, or Pamnon butterfly ; 

 the Locusta citrifolia, or lemon-leafed locust ; the Phyllium sic- 

 cifolia, or walking-leaf; the Scarabaus rhinoceros, or rhinoceros 

 beetle ; the Libellula clavata, or club-shaped dragon-fly ; and the 

 Libellula tricolor, or tricoloured dragon-fly. 



L. — Description of some new Genera and Species of British 

 Entomostraca. By W. Baird, M.D. &c. 



[With a Plate.] 



Legion BRANCHIOPODA. 



Order Lophyropoda. 



Section I. Cladocera. 



In the genus Daphnia, as elaborated by Milne Edwards in his 

 ' History of the Crustacea,^ there are two species which are so 

 anomalous in their characters that it becomes necessary to sepa- 

 rate them from the true Daphnice, and even to form a distinct 

 genus for each. These are the D. cormuta and the D. rosea. The 

 latter I have already in a previous paper (Ann. Mag. Nat. Hist, 

 xi. 87) given my reasons for removing from the genus Daphnia, 

 and constituting for it the genus Macrothrix, and the former I 

 have shortly characterized as a new genus in the ' Transactions 

 of the Berwickshire Naturalists' Club' for 1845, p. 149. 



The genus Daj)hnia of Miiller was revised by Straus in the 

 ' Mem. du Mus. d'Hist. Nat.' iv., and split into three genera, the 

 generic characters being taken from the number of joints in the 



