SUBFAMILY II. TRIDACTYLIX.E. 655 



them is as follows: Saussure, 1874, 347361, 1877, 210 22r>, 

 1897; Scudder, 1002; Blatchle.v, 1892, 1903; Morse, 1901a ; 

 K & H., 1916. 



KEY TO EASTERN GENERA OF TRIDACTYLIN.E. 



a. Species more than 5.5 mm. in length; pronotum with a weak trans- 

 verse sulcus; hind tibiae with four pairs of long slender plates used 

 in swimming; hind tarsi one- jointed. I. TRIDACTYLUS. 



oo. Species less than 5.5 mm. in length; pronotum with no transverse 

 sulcus; hind tibiae with a single pair of short plates used in swim- 

 ming; hind tarsi wholly wanting. II. BLLIPES. 



I. TRIDACTYLUS Olivier, 1789, 26- (Gr., "three" + "finger.") 



These little sand crickets are among the smallest of the 

 Gryllidae. The principal characters of the genus are given above 

 under the subfamily heading. In addition they have the head 

 subcouical; ocelli rounded, arranged in a transverse row, the lat- 

 eral ones very close to the lower inner margin of the eyes; labial 

 palpi short, robust, the terminal joint club-shaped; pronotum 

 short, somewhat shield-shaped, convex above, sides sloping, front 

 margin truncate, hind one broadly rounded and meeting in a 

 sharp angle the oblique lateral or lower one; tegmina corneous, 

 usually abbreviate, reaching middle of hind femora; wings trans- 

 lucent, fully developed, slightly surpassing the abdomen ; legs 

 strongly compressed, front pair very short, their tibiae usually 

 broad, thin, four-fingered, concave within to receive the very 

 slender two-jointed tarsi ; middle legs very slender, their tarsi two- 

 jointed and, like the fore ones, ending in a pair of long curved 

 claws ; hind tibiae with apical half bearing four pairs of long, 

 slender "natatory lamellae," preceded by slight serrations, also 

 armed at tip on each side with two very unequal spurs. Abdomen 

 slender, last dorsal segment large, deeply cleft; cerci slender, ta- 

 pering, bristly, two-jointed; beneath them a pair of slightly short- 

 er, equally slender bristly one-jointed appendages. 



Ten species of Tridactylns have been described from North 

 America. Scudder (1902) reduced these to three and founded for 

 one of them the genus EJUpes. R. & H. (1916, 283) combined the 

 two left by Scudder so that we have remaining only the one spec- 

 ies described by Say. Those reductions and combinations were 

 largely due to the paper of Morse (1901a) who showed that the 

 fore tibiae of the males vary exceedingly in form, being usually 

 more "or less irregularly ovate in outline and terminating apically 

 in four prominent equidistant teeth, with the convex outer face 

 thickly set with hairs, * * * the tarsus being inserted be- 



