49 



ray carrying about six to nine hairs; before the barred area five free tufts; a lateral 

 tuft consisting of a single hair. Anal gills long, acute, equal. 



Lateral tufts of labrum short, the inner part modified in comb-hairs, arranged 

 as a crown round the palatum which is covered with long, soft hairs. Mandibles 

 quadrangular, with two strong spines before the collar; a row of short cilia from 

 a collar and a row of about ten strong spines from margin. Dentition: four or live 

 strong teeth and before them two spines; a series of bristles below. Process below 

 distinctly furcate, with strong hair-tufts on both tips; a group of hairs at base. 

 Maxilla* subquadratic with almost straight sides, divided by a suture. On the top a 

 tuft of long, soft hairs; at its base a thorn; area between suture and inner border 

 covered by long soft hairs; inner margin furnished with a series of long, strong 

 spines. Area between suture and outer margin with tufts of soft hairs; palpe well 

 developed with four digits at top. Mentum large, high, triangular, with the median 

 tooth rather small, borders arcuate, carrying about twelve to fourteen rather small teeth. 



Colour bright grey, often milky; that of the head always yellowish red; by 

 means of this colour it can commonly be distinguished from 0. communis, with 

 which it has the structure of sipho in common; but also the more vaulted head, 

 the armature of eighth segment, and the more straight sides of the maxilla, may be 

 used as distinguishing characteristics. 



The larva has been shortly described by Meijere (1911 p. 144) by Schneider 

 (1914 p. 29) and Eckstein (1919 p. 392). The descriptions quite agree well with 

 each other and also with the above given; the number of scales on eighth segment 

 varies very much. 



Biology. More than ten years ago I had observed that, at a time when 

 0. communis had almost ceased to sting, another larger mosquito with white-banded 

 tarsi appeared. The bite of this species (0. cantans) was much worse. Everywhere 

 in the forests of North Seeland as well as in probably most of our Danish forests 

 0. cantans is extremely common in July and August; it is a well marked forest- 

 mosquito which only rarely leaves the woodlands. For more than a year I could 

 not detect, from where the myriads of these troublesome vampires came, and only 

 regular hatching experiments revealed the fact- 



In 1917 to my great astonishment I saw that all my aquaria, filled in April 

 with what I supposed was only 0. communis material, which produced immense 

 numbers of 0. communis on the first day of May, now in the time from about 

 10 /v to 25/v only produced 0. cantans. A more thorough examination of the material 

 showed that in all my cultures there were really two species of larva-, the one 

 first hatched with only one single hair in the frontal tufts, and the other, the last 

 hatched, with four and two. Also in the structure of the scales the two species 

 differed a little from each other. Testing these observations in Nature I saw that the 

 ponds after having given off 0. communis, still contained a lot of larva 1 , which almost 

 everywhere were never hatched till a fortnight later than 0. communis. In the two 

 following years the relation between the two species was more thoroughly studied. 



D. K. 1). Viilensk. Selsk. Skr., naturvldensk. og mathem. Afd. S Ra-kke, VII. 1. 7 



