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 nicobarica, or Nicobar trough-shell, or 
gaper; the Venus decussata, or decussated Venus; the Murex 
tribulus, or thorny woodcock ; the Murex rana, or frog Murex ; 
the Mytilus plicatus, or plaited muscle; the Trochus indicus, or 
Indian top; and Voluta auris Mide, 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 Scarabeus 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 
Eintomostraca. By W. Barrp, M.D. &e. 
[ With a Plate. ] 
Legion BRANCHIOPODA. 
Order Lopuyropopa. 
Section 1. 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 Daphnia, and even to form a distinct 
genus for each. These are the D. cornuta 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 Macrothriz, 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 Daphnia of Miiller was revised by Straus in the 
- *Mém. du Mus. d’Hist. Nat.’ iv., and split into three genera, the 
generic characters being taken from the number of joints in the 
