POLYMORPHA HVDROPHILIDAE PLATYPSYLLIDAE 2 I 9 



matiferous. In Berosus there are patches of aeriferous, minute 

 pubescence on the body. The pupae of Hydrophilides repose on 

 the dorsal surface, which is protected by 

 spinous processes on the pronotum, and 

 on the sides of the abdomen. 



AVe have already remarked that this 

 is one of the most neglected of the 

 families of Coleoptera, and its classifica- 

 tion is not satisfactory. It is usually 

 divided into Hydrophilides and Sphaer- 

 idiides. The Sphaeridiides are in large 

 part terrestrial, but their separation from 

 the purely aquatic Hydrophilides cannot 

 be maintained on any grounds yet pointed 

 out. Altogether about 1000 species of 

 Hydrophilidae are known, but this pro- 

 bably is not a tenth part of those exist- FIG. 101. Larva of Spercheus 

 ing. " In Britain we have nearly ninety '^^ 

 species. Some taxonomists treat the 



family as a series with the name Palpicornia. The series Phil- 

 hydrida of older authors included these Insects and the Parnidae 

 and Heteroceridae. 



Fam. 13. Platypsyllidae.--This consists of a single species. 

 It will be readily recognised from Fig. 102, attention being given 

 to the peculiar antennae, and to the fact that the mentum is tri- 

 lobed behind. This curious species has been found only on the 

 beaver. It was first found by Eitsema on American beavers 

 (Castor canadensis} in the Zoological Gardens at Amsterdam, but 

 it has since been found on wild beavers in the Ehone in France ; 

 in America it appears to be commonly distributed on these 

 animals from Alaska to Texas. It is very remarkable that a 

 wingless parasite of this kind should be found in both hemi- 

 spheres. The Insect was considered by "VVestwood to be a separate 

 Order called Achreioptera, but there can be no doubt that it is a 

 beetle. It is also admitted that it shows some points of resem- 

 blance with Mallophaga, the habits of which are similar. Its 

 Coleopterous nature is confirmed by the larva, which has been 

 described by both Horn and Eiley. 1 Little is known as to the 

 food and life-history. Horn states that the eggs are placed on 

 T Horn, Tr. Amcr. cut. Soc. xv. 1888, p. 23 ;, Riley, Insect Life, i. 1889, p. 300. 



