50 THE GENERA AND SPECIES OF BRITISH BUTTERFLIES. 
Polyommatus Alsus (the Small Blue, No. 4). This is the smallest of our native Butterflies, 
Though termed by collectors one of the “Blues,” the upper surfaces of the wings of both 
sexes are brown ; those of the male, however, having a flush of blue near the base. The under 
side resembles that of the other Polyommati. The Caterpillar of this species (No. 7) feeds upon 
the Alpine Milk Vetch (Astragalus Cicer), the Chrysalis being attached to a stem of the same 
plant. The Butterfly appears in May, and again in July and August. It is most plentiful in 
chalk and limestone districts, but is often found in some abundance in other localities. 
Polyommatus Acis (the Mazarine-Blue, No. 9). This handsome insect is conspicuously dif- 
ferent from the other species in its deep full blue, which has a satin-like gloss that gives it great 
brilliancy. The upper surface of the wings of the female are dark brown, with only a light 
purple flush towards the base. 
The Caterpillar is unknown. 
This is a rare species ; but it is in some seasons taken in some plenty in chalky districts. 
Tt appears in May and June, and again in August, being double brooded. Mr. Newman states 
that it was formerly plentiful in Herefordshire, and supposes it to be still plentiful there ; but 
Mr. Allis writes to Mr. Stainton that he knows of no capture within the last seven years. 
