1879.] 81 



is posterior and directed inward, and the inner straight side, which is 

 indurated and blackened, borders inferiorly the tymbal motor-mnscles, 

 having an inclination of about 40° to the normal vertical. The surface 

 of the enclosed membrane makes some 30° with the horizontal median 

 line, thus being inclined downward; it is also slightly directed outward. 

 In the females this chitinous frame (Trommelring) is a narrower cur- 

 vilinear triangle transversely situated. The area occupied by the 

 membrane is about one-sixth of a square inch in the males of C. pleheia 

 but in the females it barely measures one-half. Among the males of 

 a common Australian Cicada it attains 2|"' square. It has been stated 

 to be composed of a layer of elongate hexagonal or lenticular cells, 

 analogous to those of the tymbal but more delicate (Carlet, An. des 

 Scien. Zool., t. v, vi ser., p. 12). 



As in the tympana of the Acridiidee and Lepidoptera a portion of 

 the membrane is attenuated : there this part is posterior (hinteres 

 Tympanumfeld), here in the males it is neaidy central, rhomboidal, with 

 the principal axis aj^proaching the vertical close up ; in the females 

 it is cordate, situated more inwardly or nearer the apex of the frame. 

 As in Lepidopfera its superficies is conspicuous by its prismatic hues. 

 A yellow disc is surrounded by a band of lake-crimson, concentric 

 with exterior lines of purple, blue, green, yellow, and lake ; which are 

 most perfect in the male. The remainder of the membrane is of a 

 neutral tint, which appears in measure due to a fine mesh of filaments 

 that may be seen extending over the sides of the frame. The mem- 

 brane is also finely undulated as in Acridiidce, and here I think we may 

 trace the origin of the iiiterfereutial spot, with some allied sound 

 potency ; as Oscar Schmidt has already remarked. 



Toward the outer angle of the " mirror "is a brown and chitinous 

 styliform discoloration, translucent, thickened at its edges by a serrated 

 line of tubercles, attenuated, slightly angulated, with its point tangential 

 to the iridescent spot, and its opposite extremity directed towards 

 another callosity (m'), similarly tuberculated, triangular, and situated 

 on the edge of the membrane of the "mirror" near the angle. The 

 two chitinous pieces nevertheless are not in contact, but by transmitted 

 light appear connected by a slight (nervous) thread. They are not 

 specifically constant in number or shape, for in C. orni ( $ ) there are two 

 styliform pieces inclined at an angle : one traverses the iridescent spot, 

 the other separates it from the opaquer portion of the membrane. 

 Generally these chitinous pieces harmonize with those in the corres- 

 ponding membranes (Trommelfellkorpchen) of the Acridiidce and 

 Lepidoptera. 



