Mouth-parts in Plectiotarsus and ^Etlialoptera. 27 



the apex being vential ; but in riectrotarsus (and in some 

 Hydropliilitljfi and in Cliiniartlia) tlie giilar lej^ion is firmly 

 cliitinized, tiie skull is theretore complete, and tlie triangular 

 flaps are absent. The shape of the skull of Plectrotorsus is 

 unusually long, broad, and flattened dorso-ventrally (fig. 5). 

 Tenturium (rig. 3). — This is strongly d'ivelo|;ed in corre- 

 lation with the size of the heail. In structure it som what 

 recalls the tentorium of l'hri/(/anea, i. e., it consists of a cross- 

 bar at the occiput and two long endnsternites running forward 

 from it to the cl} peus. Each of these gives off a biaiich 



Fisr. 4. 



a. Mouth-parts oi Plectiotarsus ytavenhorstii (male), seen from iu front. 



Semi-dia}j;rammatic, gi-eatly enlarged. 



b. Mandible. Highly magnified. 



iJ/, mandible ; Xrt&, labium ; i^vp. hypopliarvnx; il/'P, maxillary palpus ; 

 ML, maxillary lobe ; H, baustellum ; LP, labial palpus. 



dorsally (as in Phryganea) to the roof of the skull. The two 

 long endosternites have developed broad wings for the 

 attachment of the antennary muscles. 



Antennce. — The antennse are thick, about as long as the 

 fore Vikings, the basal joint about half as long as the headj a 

 little thicker than the succeeding joints. 



