TERTAS 



Abdojien slender, arched, not quite so long as the abdominal margin of the posterior wings. 



Larva long, slender, linear, scarcely tapering towards cither extremity. 



Pur a smooth ; keeled along the back, navicular, somewhat compressed laterally, not 

 tuberculate at the sides ; the head very pointed. 



This genus was founded by Mr. Swainson in the first series of his Zoological Illustrations, Papilio Hccabc of Linne 

 being considered to be the type. Eight years afterwards, Dr. Boisduval, in his work on the Lepidoptera of North 

 America, characterised it under the name of Xanthidia ; but, I believe, at that time it was his opinion that the white 

 species of the genus as it now stands, such as Terias Albula, T. Mana, &c, should form a distinct genus for which 

 he adopted in his manuscripts the name Leucidia, but in the Species Gcnirale he abandoned this division, and adopted 

 Mr. Swainson's name for the genus, on the ground of priority. 



The species of which the genus is now composed were scattered by Godart throughout his genera Picris and Colias. 

 From Pieris, as that genus is now defined, they differ in the structure of the palpi, which are scaly, and have the third 

 joint minute, and also in their gradually thickening antenna?, and from Colias they are easily known by their having 

 pulvilli and paronychia. There is much resemblance between some of the species and the last section of Anthocharis, 

 but the antennae and the want of the red apical patch of the anterior wings are obvious distinctions. 



Three species differ considerably from the rest of the genus, but I have not ventured to separate them, because of 

 my inability to procure sufficient specimens for dissection. 



The first of these is Terias Egnatia, an insect originally considered by Dr. Boisduval as a Picris, to which genus 

 it seems more closely related by the structure of its antenna? than to Terias. Of this insect I have only had an 

 opportunity of examining the specimens in the collection of the British Museum, and consequently have been unable 

 to dissect them. This has also been the case with Terias Brephos. 



Of Terias Elvina I have been able to examine one mutilated specimen, and am unable to give so detailed a 

 description as would be required for a generic character. The feet do not differ materially from those of Terias 

 Gratiosa and its allies, but the neuration of the wings is peculiar, and will, I think, render it needful ultimately to 

 exclude this species from the present genus, and to found a new one in which probably Terias Brephos will also have 

 to be placed. The subcostal of the anterior wing throws off its first nervule at about three fourths the length of the 

 cell ; a second nervule about as far beyond the cell as its first is distant from the end of the cell ; and divides at a short 

 distance into two nervules, the lower of which I believe to be the first discoidal nervule, united for a greater distance than 

 usual to the subcostal. The cell is closed by a curved nervule, which must probably be considered as the middle disco- 

 cellular, and by a lower disco-cellular slightly curved at its origin, directed obliquely downwards and outwards, until it 

 reaches the third median nervule. At the point of junction of the two disco-cellular nervules arises a distinct discoidal 

 nervule, which I imagine to be the second discoidal nervule. The posterior wings do not differ materially from those of 

 Terias Gratiosa, the discoidal nervule being thrown off before the division of the subcostal nervule. The shoulder is 

 remarkably prominent in the males. An accurate figure of the wings will be found in the third plate, illustrative of 

 the generic characters, a comparison of which with the outlines of that of Terias Gratiosa will point out the difference 

 in structure more easily than the longest description. It is possible that the nervule which I consider as the first 

 discoidal is in reality the fourth subcostal, and that the first discoidal has become atrophied. Should Terias Elvina 

 and T. Brephos be ultimately considered to constitute a distinct genus, as I feel confident will be the case, I would 

 suggest the adoption of Dr. Boisduval's name, Leucidia, for it. 



The other species of the genus differ but little amongst themselves in structure. There is some difference in the 

 neuration of the posterior wings, as in some species the discoidal nervule is thrown off above the point at which I lie 

 subcostal nervure divides, at others immediately at this point, and sometimes it appears to be a third subcostal nervule. 

 These wings arc often angular, sometimes almost enough so to lie called tailed. The paronychia also differ in their 

 width, being much slenderer and more widely fringed with hair, in some of the white species, than in most of the 

 yellow ones. 



The prevailing colours of the genus are various shades of orange, yellow, and white ; the outer margin of the anterior 

 almost always, and of the posterior very frequently, bordered with black. The sexes often differ considerably in 



June, 1847. Y 



