On Aquatic Carnivorous Coleoptera or Dytisciclce. 195 



selves are lost amongst the general punctuation of the surface : in some cases 

 (Colpius inflatus e.g.) I fail however to find any trace of their existence, and in. 

 other cases {vide Laccophilus) they are excessively fine and indistinct, and as a 

 rule are most regular and highly developed in large and smooth species such as 

 we find in the genus Cybister ; as already remarked the outer series is more 

 irregular and less persistent than the others, the sutural series being the most 

 permanent. 



In the great tribe Hydroporides, the rule is that the upper surface of the body 

 bears a true punctuation such as exists in many other families of Coleoptera, while 

 on the other hand in the Colymbetides and Hydaticides, the opposite of this is the 

 case — punctate species being exceptional. 



When present, the punctuation is of various degrees of fineness and coarseness, 

 of density and sparsity, and is more usually seen on the elytra than on any other 

 parts ; in many of the genera of Hydroporides, however, the hind coxae are very 

 persistently punctate. The most remarkable punctuation occurs in the genus 

 Pachydi-us, where certain species have a deep coarse punctuation on the wing-cases, 

 the punctures moreover being more or less elongate in a peculiar manner. In 

 many species of the genus Hyphydrus the elytra have a double punctuation, very 

 fine punctures being mixed with considerably coarser ones. 



In the Agabini punctuation is nearly absent, the surface being either smooth, 

 or — and this is the more frequent — covered with a very fine reticulation, formed 

 by fine scratches placed so as to form meshes of irregular shape, and varying much 

 from species to species. In Copelatus the sculpture is peculiar, and in its highly 

 developed form consists of numei'ous longitudinal grooves or stri;B on the wing-cases 

 arranged in a very regular manner. In the Colymbetides the most peculiar 

 sculpture of the family is found : in Colymbetes the wing-cases are marked with 

 transverse scratches, striae or grooves, placed very near to one another, and varying 

 greatly from species to species. In Meladema {vide M. coriacea No. 978) a still 

 more remarkable sculpture exists ; the elytra bear a large number of crescentic 

 marks, which at the base are readily distinguished as such, but towards the 

 extremity of the body become somewhat changed in shape and are very densely 

 placed, so that an appearance is caused somewhat as if the surface were covered with 

 overlapping scales. 



In the Hydaticides the surface is usually smooth, but in Eretes the wing-cases 

 are marked with rather large quite round punctures, and in Acilius both the upper 

 and under surfaces of the body are much punctate. In some species of Noterus 

 there exists a peculiar punctuattion consisting of large round isolated punctures 

 placed chiefly on the hinder part of the wing-cases ; and in Synchortus there is a 

 somewhat similar sculpture, except that the punctures have their front margins 

 somewhat raised giving rise to a peculiar rough appearance. 



It is worthy of notice that when punctuation is absent from the greater part of 



TRANS. ROT. DUB. SOC, N.S., VOL. II. 2 D 



