180 MANUAL OF NATURAL HISTORY. 



more or less dilated. Feeding on animal and vege- 

 table substances in a state of decay. 



III. SUB-ORDER. WATER-LOVING BEETLES 

 (Phi%dride). 



Mandibles small, rarely exserted ; maxillary palpi 

 usually 4-jointed ; body short, convex ; elytra cover- 

 ing abdomen; hind-legs usually formed for swim- 

 ming, sometimes for walking ; fore-tibiae often spi- 

 nose. Aquatic or sub-aquatic. 



10. FAMILY. Mud-burrowing Beetles (Heteroce- 



ridae). Antennae 11 -jointed, two basal joints 

 large, the others forming an obscurely ser- 

 rated mass thickened towards the tip ; head 

 elongate, deeply inserted into thorax ; thorax 

 transverse ; body flattish ; tibiae compressed, 

 spinose. Form burrows in muddy banks of 

 ponds. 



11. FAMILY Pond -Beetles (Parnidae). Antennae 



9-jointed, the second with a lobate append- 

 age, the rest forming a clavate serrated 

 mass ; body sub - cylindric, convex ; head 

 deeply inserted into thorax ; thorax quad- 

 rate, narrowed in front ; tibiae cylindric, 

 simple ; tarsi filiform, long, 5-jointed. Bur- 

 row among the roots of aquatic plants. 



12. FAMILY. Stream-Beetles (Limniidae). Antennae 



9 13-jointed, somewhat filiform, terminal 

 joints largest, forming a club ; body ovate 

 or sub-globose, convex ; head inflexed, deep- 

 ly inserted into thorax ; thorax sub-qua- 



