﻿i870.] 255 



5. Paeactmtjs, Thomson. 



Of an oval, but very short and convex form ; mesosternum carinated, tibise 

 very strongly sphvulose. Maxillary palpi short, second and fourth joints of about 

 equal lengths, the third rather shorter. Labial palpi short, the third joint not quite 

 so long as the second. Posterior femora glabrous, and shining beneath. 



P. ceneus, the single species of this genus, has usually been associ- 

 ated with Hydrobius ; but, independently of its great dissimilarity in 

 size, it is distinguished from that genus by some evident structural 

 characters ; among these may be mentioned its much less developed 

 palpi, and its glabrous posterior femora. In general appearance, it 

 comes near the next genus, Anaccsna, from which it is distinguished 

 by its carinated mesosternum, and glabrous posterior femora. 



6. Ahacena, Thomson. 



Of a convex and sub-hemispheric, or oblong form ; mesosternum simple, tibiaa 

 strongly spinulose. Maxillary palpi short, the fourth joint rather longer than 

 either of the others. Labial palpi very short, the third joint stout, nearly as long 

 as the second. Posterior femora opaque, and densely pubescent beneath. 



This genus has also hitherto been associated with Hydrobius, but is 

 distinguished, independently of its small size, by its uncarinated meso- 

 sternum, and much less developed maxillary and labial palpi. We 

 have, I believe, three species in this country ; and, as they have been 

 nowhere, so far as I know, sufficiently described, I give below the 

 characters which distinguish them. 



1. A. globulus, Payk. Sub-hemisphericus, niger, prothoracis elytro- 



rumque marginibus dilutioribus, antennarum basi palpisgue testaceis, 

 his articulo ultimo piceo ; pedibus rufis, tarsis, praisertim posteriori- 

 bus, sat crassis. Long. \\ — If lin. 



Very common in moist, dirty places, throughout England and 



Scotland. 



This species is larger, broader, and more convex than the following, 



and has the elytra always of a darker colour, except at the margins, 



and the tarsi are stouter. 



2. A. variabilis. Subovalis, c&nvexus, capite nigro, palpis piceis, arti- 



culo ultimo nigro, antennarum basi testaceo ; prothorace piceo-nigro, 

 lateribus dilutioribus, elytris vel piceis, vel piceo-testaceis ; pedibus 

 piceo-rufis, tarsis gracilibus. Long. 1\ — 1\ lin. 



Var. capite utringue macula parva ante oculos rufo-testacea. 

 Common in England, rare in Scotland. 



