178 Ayinals Entomological Society of America [Vol. IX, 



The number and arrangement of these carinae on the ventral 

 surface of the ninth abdominal segment present considerable 

 variation. Forbes ('10, p. 222) states that this pupa is similar 

 in general form to that of N. obscuralis ' ' but of the seven ridges 

 near the tip of the abdomen beneath, only the central one 

 remains". The writer has examined a large number of these 

 pupae during the past five summers and has failed to find a 

 single pupa which possessed only the single, median carina. 

 The first pair of lateral carinae is always present in addition to 

 the median one and, as stated above, there is sometimes present 

 a second pair laterad of the first. When a second pair is present, 

 the component carinae are usually smaller than the other 

 carinae and not so readily distinguished. In TV. obscuralis, as 

 described by Hart ('95, p. 173), the first group of elevations are 

 described as follows: "Apex of abdomen subacute; ninth seg- 

 ment beneath with a faint elevated line at middle, and a small 

 elevation each side." In the figure accompanying this descrip- 

 tion, the "small elevation each side" is represented as circular in 

 contour. This condition seems distinctly different from that 

 existing in N. maculalis since, in all of the pupae examined, the 

 single elevated line, when present, is unaccompanied by conical 

 elevations of any sort, and when absent, it is represented by a 

 pair of similar, longitudinal elevations. Furthermore, this 

 group of elevations is on the eighth abdominal segment. The 

 above description probably does not include all of the variations 

 which exist since the writer found one specimen in which the 

 anterior group of carinae consists of three pairs of elevations, 

 diminishing in size on either side. 



Caudad of the second group of carinae is a distinct Y-shaped 

 impression. Forbes ('10, p. 222) makes the following state- 

 ment: " and the anal opening is not distinctly 



Y-shaped." All of the specimens examined in this connection 

 show this ventral impression to be of such structure that the 

 expression "Y-shaped" describes it quite well. 



As already stated, the full-grown larva usually attaches its 

 case to the lower, submerged surface of a water-lily leaf and 

 transforms into the pupa. Just before pupation, a dense, 

 whitish, apparently complete, silken covering is spun around the 

 larva. This silken covering adheres closely to the inner walls 

 of the case and is strongly attached at the periphery. It is 



