Ilydrophiliwv..'] iiydropiiilid.k. 219 



absent in the larvre of the Sphjeridiinaj : all the species arc aquatic, but, 

 "with few exceptions, they are very poor swimmers ; as jNIulsant ol)serves 

 (Palpicornes, p. 13), it is quite sufficient to see their motions in the water 

 to lie convinced of their pacific and non-predaceous habits. They may 

 be divided into the following tribes : — 



I. Second joint of posterior tarsi elongate, longer than tLird. 

 i. Thorax at base as wide as base of elytra, smooth. 



1. Tarsi compressed ; metasternuni prolonged into a spine . Htdeophilina. 



2. Tarsi not compressed ; uietasternum not prolonged into a 



spine HroKOuiiNA. 



ii. Thorax narrowed behind, narrower than elytra, furnished 



with distinct longitudinal furrows IIelopuouina. 



II. Second joint of posterior tarsi short, about equal to third. 



i. Clypeus emarginate ; scutelluin long, triangular ; anterior 



coxal cavities open behind Spekchkixa. 



ii. Clypeus truncate ; scutellum small and short ; anterior coxal 



cavities entirely closed IIvDiiOCUiNA. 



HYDROPHILINA. 



The two species belonging to this tribe are 1)3- far the largest of the 

 British Palpicornia, and the best swimmers ; they belong to separate 

 genera. 



1 . Prosternum plainly excavated ; metastcrnal spine prolonged 



considerably beyond posterior coxa; ; length 37-48 mm. . . IIVDKOruiLCS, (7eq/^. 



2. Pj-osternum sharply keeled ; metasternal spine hardly pro- 

 jecting beyond posterior coxai ; length 14-18 mm. . . . Hydrochabis, Lair. 



KYDROPKIX.US, Geoflfroy. {ITijdrous, Leach.) 



This genus cunq)rises about forty species, which are widely distributed 

 tliroughout the globe, but are chiefly found in hot climates ; they are 

 remarkable for their large size ; they are usually black or olive-coloured, 

 but some exotic species are metalhc : the females construct a cocoon iu 

 which to shelter tlieir eggs. 



K. piceus, L. Oval ; l>lack or olivaceous black above willi the 

 margins of the elytra greenish ; head smooth with some deeply punctured 

 depressions ; thorax smooth with a deep and deeply punctured depression 

 on each side of middle in front ; elytra with rather finely punctured 

 strire, alternate interstices with rows of large punctures, duller in the 

 female than the male, furnislied in both sexes with a sharp spine at the 

 sutural angle ; breast clothed with yellowish pubescence, alulomen black 

 with yellowish spots at sides ; antenna^ and legs black or pitchy ; male 

 willi tlie onychium (the last joint of tarsi bearing the claws) dilated into 

 a larg(» triangular plate : this sj)ecies, witli tlie exception of Liicanxs 

 o'l-riis, is the largest of our indigenous Coleoptera. Long. .37-48, lat. 

 19-22 mm. 



This species is extremely local, and appears to be almost confined to the London 

 district and adjoining counties, and to certain portions of the fen districts ; it is not 



