XXIV INTRODUCTION. 



the hind legs assume the form of oars in Dytiscidse and some 

 Hydrophilidae; or the middle and hind legs become short, broad, 

 and flat, as in Gyrinidas. At the extremity of the tibia; are two 

 movable spines, called tibial spurs; one or both of these may be 

 entirely absent. 



The tibifE of the Rhynchophora are for the most part without 

 spurs, but the tip has certain peculiarities of structure requiring 

 special mention. The tip is often prolonged internally forming 

 a hocrk of variable size; when this prolongation is from the inner 

 apical angle the tibia is called miicronate, as in Sphenophorus, 

 when from the outer angle, unguiculale, as in Cossonus. The 

 articular cavities are not always at the tips of the tibias in Rhyn- 

 chophora, but often on the inner side above the tip; in the latter 

 case the tip of the tibia is often truncate, forming a more or less 

 oval space surrounded by short fimbriae, called the corhd ; when 

 this oval space is thus complete the corbels of the tibiae are called 

 closed; when, however, the articular cavity extends to the tip 

 and the oval space is obliterated, the corbels are open. 



Attached to the tibiae is a series of from one to five pieces, 

 constituting the foot, or tarsus; the last joint usually bears two 

 claws, which, by ^ very rare exception, are sometimes wanting. 

 The genns Phanseus and the family StylopidfE a.re the only 

 examples in our fauna in which this is the case ; in the males of 

 some Phanceus the anterior tarsi are entirely wanting. The tarsi 

 vary greatly in the nural)er of joints as well as in their structure. 

 The greatest number of joints is five, and when one disappears 

 it is usually lost on all the tarsi at the same time; from this the 

 older authors took their basis of subdivision of the Coleoptera; 

 those with five joints being called peutamera, with four tetrarnera, 

 with three trimera, and with two dimcra. A large series, how- 

 ever, has five joints on the anterior two pairs of feet, and four 

 on the hind feet, these are called heteromera. These divisions 

 have been in great part abandoned for a more natural arrange- 

 ment of the families. Instances occur in the Clavicorn series in 

 which the usual pentamerons tarsi become heteromerous in one 

 or other sex; when the hind tarsus becomes 4-jointed it is usually 

 in the male, when the anterior, the character is generally female. 

 Rarely in some Clavicornia the anterior tarsi alone are 5-jointed, 

 the other two pairs 4-jointed. 



The tarsal joints vary in form, and may be slender and cylin- 



