18 RHOPALOCERA. 
district northwards to Chontales, in Nicaragua, Thyridia melantho must certainly be 
very abundant. 
A little variation exists between individuals of this species: in some examples the 
proximal discocellular spot of the primaries is almost obsolete; in others the distal 
spot is scarcely visible, the whole basal half of the wing being nearly uniform black ; 
in one specimen from Chiriqui the black apical angle of the secondaries embraces the 
black spot at the end of the cell. The nearest ally to Z. melantho is undoubtedly 
T. edesia, which takes its place in the northern portion of the southern continent, 
being abundant in the neighbourhood of Santa Marta and the western provinces of 
Venezuela. . 
Our figure is taken from the type specimen (a male) sent us from Panama. 
MECHANITIS. 
Mechanitis, Fabricius, Ill. Mag. vi. p. 284 (1807) ; Doubl. & Hew. Gen. Diurn. Lep. p. 128; 
Bates, Trans. Linn. Soc. xxtil. p. 528. 
Tarsus of front legs of female with four joints, a pair of spurs on each of the second 
and third joints; primaries with recurrent nervule on lower discocellular; secondaries 
with recurrent nervule on middle discocellular; costal nervure of secondaries of female 
anastomosing with subcostal about the middle of the costal margin of the cell; cell of 
secondaries not extending nearly to the apical angle. 
Five tolerably well-marked races of this genus are found in Central America, all of 
which have received names; but an examination of a large series of these insects, we 
think, shows that, though in certain districts particular forms prevail, specimens are not 
wanting tending to link most if not all of them together. In fact we find that the 
representatives of Mechanitis in Central America present the same features as regards 
their variation as those possessed by the insects found in the valley of the Amazons, so 
fully discussed by Mr. Bates in his paper in the ‘ Transactions of the Linnean Society.’ 
The geographical distribution of these different races in Centra] America is an 
instance of how races may be nearly, but not absolutely, confined to particular localities. 
M. doryssus, by far the most widely distributed of them all, attains its maximum 
development in Guatemala, where it is most abundant. It is found in Mexico, where 
it is the sole representative of the genus; towards the isthmus of Panama it becomes 
quite rare, its place being taken by J. macrinus. It then reappears in a slightly 
modified form in the northern portions of South America. 
M. lycidice is also abundant in Guatemala, but becomes rare in the southern portions 
of the isthmus, its place being taken by MV. isthmia, a race from which it is but 
imperfectly segregated, an almost complete series of intermediate steps being found to 
connect the extreme forms. The well-marked yellow cross band seen in many indivi- 
