224 FRESH-WATER AQUARIA. 



its specific name. It is frequently found in brackish 

 water. 



The small beetles classified under the head Rydrochus are 

 not more than iin. long, but generally less. They have long, 

 narrow bodies, seven-jointed antennae, prominent eyes, and 

 their elytra are very glossy and beautifully coloured. R. 

 angustatus is perhaps the commonest of the four species of 

 the Hydrochi, and is really a beautiful little insect, with 

 its very glossy, greenish-black wing-cases. Its thorax, which 

 is narrower than the elytra, is deeply punctured, and its 

 legs and antennae are reddish. 



The little beetles belonging to the genus Laccohius are 

 divided into the species L. minutus and L. nigriceps. They 

 are rather less, most of them, than |in. in length, and are 

 yellowish- grey in colour. The Laccobii are by no means rare. 



The very tiny beetles coraprised under the head Ochthebius 

 are frequently found crawUng under or over stones which are 

 half out of the water. Some of these insects are so small 

 that they are not more than ^^in. in length. Their antennae 

 are nine-jointed, the five terminal joints forming a club. 

 Their bodies are elliptical, their elytra of a glossy metallic 

 colour, and their legs short. Of the ten species included 

 in this genus, 0. pygmceas is one of the commonest. It is 

 about xsin. in length, and of a bright metallic-brown colour. 

 The thorax is deeply punctured, the legs are reddish, and 

 the palpi and antennae of a lighter colour with darker 

 tips. 



The beetles of the genus Rydrmna have the same habits 

 and habitats as those of the preceding. They are chiefly 

 noticeable for the extreme length of their palpi, which almost 

 equal in length half of the body. Their antennae are seven- 

 jointed, the last four of which form an oval club. The elytra, 

 which are mostly of a bright black colour, do not cover all 

 the abdomen. The thorax is broad across the middle, 

 and gradually tapers towards the anterior and posterior 

 margins ; the legs are long. R. riparia is one of the most 

 abundant of the six species of the HydraenK. It is a narrow, 

 shining, black insect, having rather a long head, and the 



