MECHANITIS. 129 



Anterior Legs of the male exceedingly minute ; the tarsus and tibia represented by a small ovate 

 knob. Anterior Legs of the female with the femur rather longer than the tibia, which is nearly 

 cylindric, but rather thickened at the apex. Tarsus but little more than half the length of the 

 tibia, in general of uniform size to the last joint ; its first joint about double the length of the 

 rest combined ; the second short, about one fifth as long as the first ; the third rather shorter ; 

 all furnished with delicate scattered spines ; the last only with a pair of stout spines at the apex, 

 covered by a tuft of hairs on the lower surface of the small, very short, obliquely truncate fourth 

 joint : sometimes rather clavate ; the basal joint about double the length of the rest combined ; 

 the second and third thicker, nearly equal in length, both being about one fifth the length of the 

 first ; these three joints each with a pair of strong spines at the apex, covered by a tuft of hairs 

 on the succeeding joint ; fourth joint very short, transverse ; fifth almost anchylosed with the 

 fourth, conical, mucronate at the apex. 



Middle and Posterior Legs tolerably stout. Tibia! much longer than the femora, very spiny ; the 

 spurs distinct. Tarsi about as long as the femora, spiny ; the spines at the sides very closely 

 placed, and longer than the rest. Basal joint about equal to the rest combined ; second rather 

 more than one third the length of the first ; third about two thirds the length of the second, all 

 these nearly cylindric ; fourth short, rather flattened, widest at the apex ; fifth oval, elongate, 

 equal in length to the third, rather flattened. Claws small, much curved, grooved below. 

 Paronychia with the outer lacinia almost as long as the claw, slender, strap-shaped ; the inner 

 lacinia shorter, subtriangular. Pulvillus jointed, about equal in length to the claws. 

 Abdomen clavate, very elongate, extending far beyond the posterior wings. 



Larva and Pupa unknown. 



Mechanics differs from all the preceding genera in the structure of the posterior wings, the median nervure of which 

 appears to be four-branched, the discoidal nervure being united to its third nervule in such a manner as to seem to 

 form a fourth ; a structure precisely analogous to that of the anterior wings of the Papilionida3. In addition to this 

 character, there are others which also serve to discriminate it from its nearest neighbour Ithomia, some species of wliich 

 much resemble it in colour ; these are, the different proportions of the wings, of the joints of the palpi, aud of the tarsi, 

 the anterior ones in the females especially, and the somewhat different antenna?, 



The most remarkable peculiarity in the genus is the sexual variation in the neuration of the anterior portion of the 

 posterior wings, the aberration from the normal structure occurring in the females, a circumstance so extremely rare, as 

 to have led me at first to doubt the entire correctness of my observations. Careful and repeated examinations of a vast 

 number of specimens of both sexes of many species have satisfactorily proved the fact, that all the specimens which 

 have the costal and subcostal nervures united in one as far as the middle of the wing are females ; and this structure 

 never occurs in the males, in which these two nervures, though sometimes running nearly parallel, and but little distant, 

 are still perfectly separated from one another from the point where the precostal is thrown off. In one section both 

 sexes have the nervures separated from this point. 



The structure of the anterior tarsi differs in the two groups into which this latter section is divisible, but only in the 

 females. In the one group, as in the first section, they are equal in thickness throughout, and only the third joint 

 bears the usual strong apical spines ; in the other, the second, third, and fourth joints are rather broader than the first, 

 and the first, second, and third joints all have the apical spines. 



The predominant character of the colouring in this genus is the same as in the last group of the true Heliconi;u, and 

 there are some instances in which the markings are almost identical. The two genera, however, can never be 

 confounded by any one who pays attention to the neuration of the posterior wings. 



December, 1847. N N 



