204 



INSECTS OF SAMOA. 



strongly dilated ; posterior tibiae short, fitting closely into inner surface of 

 corresponding femora ; tibia (Text-fig. 15k) gradually broadening towards 

 apex, which is drawn out into a point, its surface being somewhat convex 

 proximally, and somewhat concave at broadest part ; tarsus arising from a 

 point on concave surface distant from apex ; tibial spur greatly enlarged so 

 as to form a thick club-shaped process, surface of which appears ridged ; lateral 

 margins of process sinuous, outer margin more so than inner ; tarsus almost 

 as long as tibia ; claws appendiculate. 



Length, 3 J mm., greatest width, 2| mm. 



Tutuila : Pago Pago, 30.ix.1923, 1 example (type) (Swezey and Wilder). 

 Leone Road, 7.ix.l923, 1 example (Swezey and Wilder). 



Type in the British Museum ; paratype in the Bishop Museum. 

 Described from two examples. 



It will be noticed that the form of the hind tibia (cf. j, k, Text-fig. 15) in the 

 genotype of Sphaerophyma differs from that in the present species, but the tibial 

 processes in both cases are similar in form and structure, i.e. in the possession 

 of ridges on the surface. In other structures considered collectively S. insularum 

 resembles the genotype, and I therefore consider the difference in the form of 

 the hind tibia as specific ; examination of further material may alter this view. 



In determining the relationship of this species it was found necessary to 

 make a comparative study of the structure of the posterior legs of insects 

 belonging to the genera dealt with below. In these the insects show special 

 modifications of the hind tibiae, which possess taxonomic value. As a result 

 of the study the following general statements have been framed and the 

 characters analytically shown in a table, accompanied by illustrations. 



(1) The posterior femur is enormously dilated, and is held pressed against 

 the abdomen, where a depression has been developed on the ventral surface. 

 The outer edge of the femur is broadly rounded, and the inner has a slight 

 concavity for the reception of the corresponding tibia. 



(2) The tibia is always short, never exceeding the length of the inner side 

 of the femur. It is narrow and cylindrical near the point of articulation with 

 the femur, whence it gradually broadens towards the apex. It is a solid structure, 

 having an upper and a lower surface, and two lateral margins, that nearer the 

 body being termed the inner and the other the outer margin. The upper surface 

 is flat, or somewhat convex, and without hairs, while the lower is semicylindrical, 

 often with a clothing of hairs, more especially near the tip. The lateral margins 



