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Lateral tufts of labrum extremely short, the inner part with short comb-hairs; 

 palatum feebly developed with short hairs. 



Mandibles quadrangular with two curved spines before the collar; a row of 

 rather short cilia from a collar; about seven to ten thorn-like bristles from mar- 

 gin; dentition five, almost equally strong teeth and before them a strong tooth; 

 long cilia below thorns; process below very indistinctly furcate with hairs on both 

 tips and a group of hairs at base. 



Maxillae of remarkable form, broader than long, on apex a brush of long hairs, 

 which was commonly spread out as a flattened crown over the maxilla, all the 

 hairs lying in the same plane but with the hairs turning towards the inner surface 

 of the maxilla much longer than on the outer edge; near the inner margin a thick 

 and coarse coating of short soft hairs; inconspicuous thorns along the margin. 

 Palpi remarkably well-developed, almost cylindrical, furnished with four digits at apex. 



Mentum triangular with middle tooth feebly developed and thirteen teeth along 

 the borders. 



Biology. From one of the Hydrophantes ponds in Hestehave near Hillerod 

 0. excrucians and commnnis were hatched in 1919 in huge numbers. Among the 0. 

 communis material a good many were characterized by brighter bands, rusty in the 

 middle on the abdomen, and almost white, long joint in the palpi of the male. I regarded 

 them as an aberrant form of O. commnnis, but sent them to Mr. EDWARDS who kindly 

 told me that according to his opinion they were 0.' prodotes Dyar. 



On examining my larva material from the Hydroplantes-pond I found a few 

 specimens of a highly characteristic larva, hitherto overlooked by me. Next year, 

 just after the ice had melted very many of these larvse were found and later on 

 hatched in my aquaria. Having found the species in this single pond I searched 

 for the larvse in a great number of ponds near Hiller0d, but found the species only 

 in a few of them and always in small numbers. On the other hand, on an excur- 

 sion in April to the many ponds on the Eremitage-plain in the Royal Deer Park 

 about 15 kilom. from Copenhagen, almost all the ponds teemed with 0. prodotes 

 larvse, and in more than one of the ponds I only found this very same species. 



The species is hatched very early before 0. communis and 0. nemorosus. On 

 examining the ponds in the latter part of April and first days of May the ponds 

 contained huge masses of larvae of these two species but not a single O. prodotes- 

 larva. It is owing to this fact that I have overlooked the species in 1917 1919. 

 As far as I have hitherto observed, it seems that the species prefers temporary 

 ponds on plains, not overshadowed by trees, or ponds lying on the outskirts of 

 forests; I have never found them in the temporary pools in the deepest parts of 

 the woods, overshadowed by trees and only rarely touched by the sunbeams, locali- 

 ties where 0. communis preponderate. 



The species has unquestionably only one generation in the course of the year, 

 lying almost the whole year as eggs; all ponds in which the species is found are 

 commonly dry from June to March. The eggs according to DYAR (1920 p. 10) have 



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