1916] Forbes — On the Tympanvm of Certain Lepidoptera 191 



grouped, and no reason has developed to separate them widely 

 from the preceding group. 



5. The Bombyeidse, Lasiocampidte, Saturniidse, Sphingidse, 

 Apatelodes, and their relatives also form a distinct group, but as 

 they are associated by the absence of specializations in the struc- 

 tures studied, they may be justly divided up on other characters. 



6. The tympanic bulla of the Geometridse is not homologous 

 with that of the Arctiidte, etc., being developed on the opposite side 

 of the spiracle. 



7. A new subfamily, Civieliinw, is needed for the genus Cimelia, 

 based mainly on the following characters: Tympanum absent; 

 Sc of hind wing not angulate at base, without a brace connecting it 

 with the base of the frenulum, closely parallel to R to a point well 

 beyond the end of the cell. Structure otherwise as in the lowest 

 Geometridse (OEnochrominse) . 



Supplementary Note: Since writing this article, the Diop- 

 tidse, Thyatiridee, and Drepanidse have been examined. The 

 Dioptidse show no tympanum of any kind and will make a first 

 exception to the rule that uniordinal hooks on the prolegs are co- 

 ordinated with a tympanum of Arctiid or Noctuid type. The egg 

 is described as spherical, and so may be of either type. In the 

 Thyatiridse and Drepanidse there is a new type of tympanum; 

 the tergopleural suture is modified into a large cavity, opening 

 backward, which lies beneath the spiracle, and there is a large 

 double chitinized structure subventrally which does not open to 

 the exterior unless it communicates with this tergopleural opening. 

 The structure is so complex, and so similar in the two families as to 

 make their association almost certain, especially as the larval and 

 venational characters are rather similar. 



Explanation of Figures. 

 A = Lower edge of subdorsal muscle with nerve-supply. 

 AS A^ = First and second segments of abdomen. 

 A^ ant. n. = Anterior nerve trunk of first segment of abdomen. 

 B = Supposed sensory end organ of tympanum, 

 conn. = Connective, 

 ex. = Coxa. 



epm. = Epimeron (of metathorax) . 

 eps. = Episternum (of metathorax) . 



