104 ENTOMOLOGISK TIDSKRIFT IOII. 
Tarserna leda däremot snedt nedat mot tibierna och 
likaså klorna, sa att dessa aro riktade rätt nedåt. Själfva 
kloleden har en egendomlig struktur, som synes hafva till 
uppgift, att halla klorna fast i en vinkelrätt nedåtböjd ställning. 
Framkanten pa tarsen ar nämligen pa undersidan utbil- 
dad till ett par snedt mot hvarandra stallda tjocka skifvor, 
hvars inre sida ar refflad, (Fig. 10). Vid basen af kloleden 
pa undersidan synes en hög, i omkrets oval kudde, som 
ocksa ar refflad och som begransas pa sidorna af tva tunn- 
väggiga strimmor. Nar nu klon böjes nedåt, pressas sanno- 
likt denna kudde ned emellan tarsens skifvor, hvarest den 
kvarhalles af refflorna, sa att den blir last fast i denna stall- 
ning. Djurens förmåga att trycka sig sa tätt till stenarne 
torde atminstone delvis bora tillskrifvas denna mekanism. 
Summary. 
Two nymphæ were found by D:r I. Arwipsson in the stomach of 
two young salmons in Lagan (county of Halland). An account is given 
of the literature refering to the species and of the errors as regards its syste- 
matic position to which its exceptional shape has given rize. The external 
morphology is described and illustrated by original drawings. In the follo- 
wing respects the interpretation of the structures differs from Vaysszére’s views, 
besides which the following additions are made. Mouthparts. Attention 
is called to the resemblance between the mandibles of P. and of Campodea. 
The existence of a mentum is pointed out. The maxilla have primitive 
features, as pointed out by V.-Thorax, Pronotum probably not fused with 
the mesothoracal plates i. e. Ist pair of wings, but only hidden by the 
anterior edge of them and partly reduced. Metasternum demarcated from 
mesosternum by a fine line. At the sides of the sternum there are 3 small, 
rectangular plates of which, however, only the anterior one is demarcated 
all round by sutures, whereas the other two are open posteriorly and flanked 
by slightly raised lines, not real sutures. The anterior plate, which takes 
part in the formation of acetabuta I is probably an epimeron; the other two 
are interpreted as superficial structural adaptations to form resting grooves 
to the femora II and III, when pressed close to the body. What V. con- 
siders as epimera is in reality the ventral side of the flattened margin of 
the mesothoracic plates. Abdomen. On the ventral side only 9 abd. 
segments are discernible, but, if V:s. statement holds good, the Ist pair of 
trachéal gills represents the rest of a greatly reduced Ist abd. segment. The 
reduction af this — compared with the presence of 10 abd. segments in 
other Ephemeridæ — is probably a result of the concentration and fusion 
of the anterior abd. segments which has taken place in connection with the 
formation of the respiratory chambers. Food. The food of the nymphe 
does not consist of infusoria and vegetable and animal detritus as V be- 
lieves, but they are carnivorous, devouring larva of Chironomide, especially 
Tanytarsus, which are swalloved entire. Perfection of adoptation. The 
fact that only 2 specimens where sound amongst the contents of the sto- 
machs of 148 salmons, compared with the great number of nymphe of other 
Ephemeride, Phryganide, Plecoptera and Jarve of Chironomid@ is a proof 
that Prosopistoma is admirably well adopted to escape the salmons. 
iene 
