90 



whitish ; on the front marginal ridge of the second segment oc- 

 cur two orange spots and two black spots in front of them close 

 to the head, and between these pairs of spots is the concealed ori- 

 fice from whence the retractile soft fleshy horns of pinkish-red 

 color dart forth when irritated, and when seen at this period are 

 uniformly stout, with blunt diverging extremities; the ground- 

 color of the smooth skin of the body is a very brilliant pale yel- 

 low-green, becoming white on the belly and ventral feet, the 

 segmental divisions widely banded with deep purplish edged 

 with velvety-black, and across the middle of each segment is a 

 broad velvety-black band covered with excessively fine bristly 

 pubescence, and bearing the orange tubercle of the upper row 

 near the front margin, and sometimes also that of the middle 

 row ; but generally this transverse black band is interrupted by 

 an isthmus (so to speak) of the ground-color which bears this 

 tubercle ; and below there is always a slanting isthmus of ground- 

 color bearing the lower tubercle ; on the third and forth seg- 

 ments the broad bands have only this lower interruption, and 

 bear the orange warts of the two upper rows (here diminished in 

 size) in their middle ; the anterior legs are white with black tips 

 and joints ; the ventral legs have each a narrow streak in front, 

 a spot behind, and a large crescentic mark of black above the 

 white feet, which have dark hooks ; on the anal legs this black 

 mark is purplish in the middle; the spiracles are blackish-slate 

 color situate within the lower parts of the black bands ; the 

 whitish belly has a central series of blackish blotches, and narrow 

 transverse bands in the deeply sunk divisions. 



The pupa, when come to its full color, is pale yellow on the 

 back and abdomen, and delicate light green on the head and 

 wing-covers. 



Ensworth, Februaiy 28, 1882, 



WHAT CONSTITUTES A SPECIES IN THE GENUS 



ARCTIA? . 



By R. H. Stretch. 



I have recently drawn some fifty figures of insects be- 

 longing to the genus Arctia as a portion of the illustrations to 

 my synopsis of the North American Bombycidae, and in the case 

 of our Californian A.achaia, G. and R., have been compelled to 

 give no less than twelve figures to illustrate even partially the 

 variations to which it is subject. I confess myself utterly at a 

 loss to frame a description of the species which shall enable the 

 incipient student, with only one or two specimens before him, to 

 recognize the insect without the aid of figures. 



What may be considered a typical specimen has the prima- 

 ries black, with the markings ranging from pale ochre to cream 



