724 Mr. Gilbert J. Arrow on 



cavity is smaller, more sharply defined and more finely 

 sculptured, and the coxa is provided at the corresponding 

 part with a series of plectra consisting of oblique rows of 

 short and strung chitinous crests. The similarity between 

 the vocal apparatus of the Heliocopris and Taurocerastcs 

 forms may indicate a relationship greater than has been 

 supposed to exist between them, each being of a rather 

 primitive type. 



In Orphnus and the genera directly related to it sound 

 is produced in the same region but by a rather different 

 means. The hind coxae are expanded in these beetles and 

 overlap the abdomen behind, and near the outer end of the 

 flattened inner side is a rather broad and slightly convex 

 area which is delicately ribbed in the direction transverse 

 to the axis of the body. The hinder margin of the cavity 

 receiving the coxa forms an acute edge for scraping this 

 vibratory plate. In the common Old World genus Orphnus 

 the plate is large and rectangular, and the lip of the cavity 

 appears to be supplemented by two other sharp edges 

 placed within it. In Hyhalns, which represents the family 

 round the shores of the Mediterranean, the plate is very 

 large and occupies nearly the whole outer half of the coxa 

 beneath. In the New VVorld representative, ^gidncm (PI. 

 XXXVI, fig. 10), although the beetles are larger and the 

 hind coxffi more dilated, the vocal area is reduced to a much 

 smaller semi-elliptical space. In the new genus to which 

 I have given the name of /Egidinus it is elongate, narrow- 

 ing at both ends. Indeed stridulation is probably general 

 throughout this small family, although it has not hitherto 

 been recorded. Mr, Guy Marshall, however, informs me 

 that he has noticed the sound uttered by species of 

 Orphnus inhabiting Mashonaland. Another allied genus, 

 of which, by M. Kene Oberthtir's kindness, I have been 

 able to examine one of the only two known examples, is 

 Sissantobms, in which the same apparatus is present, as 

 shown by the characteristic form of the coxse. 



In a very remarkable new genus inhabiting the same 

 region of Patagonia as Frickius and to which I have given 

 the name Idiostoma, the posterior coxaa are scarcely at all 

 flattened, but very thick, and the striated instrument 

 therefore traverses a convex surface (PI. XXXVI, figs. 1, 

 la). It forms a long and narrow rope-like prominence 

 agreeing in its situation with the instruments just de- 

 scribed, although the relationship of the two species iu 



