ORTHOPTERA OF INDIANA. 413 



has written of it as follows: "Our common mole cricket usually be- 

 gins its daily chirp at about four o'clock in the afternoon, but stridu- 

 lates most actively at about dusk. On a cloudy day, however, it may 

 be heard as early as two or three o'clock; this recognition of the 

 weather is rather remarkable in a burrowing insect, and the more so 

 as it does not appear to come to the surface to stridulate, but re- 

 mains in its burrow, usually an inch below the surface of the ground. 

 Its chirp is a guttural sort of sound, like grii or greeu, repeated in a 

 trill indefinitely, but seldom for more than two or three minutes, 

 and often for less time. It is pitched at two octaves above middle 

 C, and the notes are usually repeated at the rate of about 130 or 135 

 per minute; sometimes, when many are singing, as rapidly as 150 

 per minute. Often, when it first begins to chirp, it gives a single 

 prolonged trill of more slowly repeated notes, when the composite 

 character of the chirp is much more readily detected, and afterward 

 is quiet for a long time. When most actively chirping, however, the 

 beginning of a strain is less vigorous than its full swell, and the 

 notes are then repeated at the rate of about 120 per minute; it 

 steadily gains its normal velocity. It sounds not unlike a feeble 

 distinct croak of toads at spawning season." 



LII. Tridactylus Olivier (1789). 



To this genus and the next belong the "sand crickets" which are 

 among the smallest of the Gryllidae, no one of the three species found 

 in the United States being more than 10 mm., or two-fifths of an 

 inch in length. The principal distinguishing characters of the genus 

 are given in the key to the genera of Gryllotalpince. 



The fore tibia of the males of Tridactylus has been shown by 

 Morse to vary much in structure. It is usually more "or less irregu- 

 larly ovate in outline and terminating apically in four prominent 

 equidistant teeth, with the convex outer face thickly set with hairs, 

 * * * the tarsus being inserted between the first and second teeth 

 and lying on the anterior face." From this normal form it varies in 

 progressive degree to a remarkably bifurcate organ in which the 

 inner limb is elongated and devoid of hairs, the innermost tooth 

 nearly disappears, the second is greatly prolonged into a claw-like 

 organ, while the femur acquires tooth-like projections on its upper, 

 inner ventral angle and becomes greatly enlarged. The outer wings 

 or tegmina are horny and opaque and do not reach the end of 

 the abdomen, while the inner wings are longer and folded length- 

 wise like a fan. The hind femora are much enlarged and the insects 

 are active leapers. 



