NORTH AMERICAN ODONATA. 157 



The mandibles are moderate in size, but strong, and toothed on the 

 inner (opposed) surface. The apex ends as a sharp point, on both 

 anterior and posterior sides of which is an acute tooth. Separated 

 by an interval from this apical group of teeth, is a toothed basal 

 portion, suggesting, as Rambur remarked, a molar. In surface view, 

 this is a Z-shaped ridge. If the top of the Z be considered to be 

 that lying nearer the apex of the mandible, then the upper angle of 

 the Z lies next the anterior surface of the mandible, that is, the Z 

 looks backwards. At each of the two angles, and at each of the 

 two free ends of the Z, the ridge is elevated into an acute tubercle. 



I'he stem of the first maxilla is composed of two joints of which 

 the basal is the cardo, the distal, about twice as long, is the stipes. 

 Articulated to the distal end of the stipes are two separate pieces, 

 each consisting of a single joint. The outer is much the slenderer, 

 of simple form, clothed with hairs, is curved inwards and backwards, 

 and ends jn a fairly acute apex ; it is the maxillanj paljyus. The 

 inner piece is flattened from behind forwards ; its inner edge bears 

 six long spines and some long hairs ; it corresponds to the galea and 

 lacinia (outer and inner lobes of the maxilla) fused together (Ger- 

 staecker 2*). 



Various views have been held as to the composition of the labium 

 or second maxilla. It will be sufficient to mention only two here. 

 An examination of PI. II, fig. 7, will be necessary to properly un- 

 derstand the text. 



By Eambur (33), and in the earlier writings of Hagen, the median portion of 

 the labium {ml, fig. 7) was regarded as representing the inner and outer lobes 

 of the labium, that is a fusion of the glossae and paraglossse, while each lateral 

 portion (II) was held to be merely the labial palp. 



Gerstaecker (2) holds that ml is a fusion of merely the inner lobes (glossse), 

 while II is composed of a union of an outer lobe (paraglossa) and a labial palp. 

 Graber (Die lusekten I, p. 130, fig. 186) accepts Gerstaecker's view, but piece s, 

 which Gerstaecker calls the squama, he regards as half of the mentum ; hence m, 

 the " mittelstiick" of Gerstaecker, or subglossa, has come to lie between the right 

 and left halves of the mentum. 



For the sake of convenience, de Selys' usage will be followed here, 

 and the middle portion, ml, be designated as the median lobe, and 

 each lateral part, II, as the lateral lobe. The median lobe is bifid at 

 its extremity in the Agrionida?, some Gomphiuse, and the Cordule- 

 gasterinse ; it is entire in the other groups, in the Aeschninse a me- 



* These figures ^fter authors' names refer to papers named in the bibliography 

 with which Part I concludes. 



TKANS. AM, ENT. SOC. XX. JULY, 1893, 



