1929] Structure and Significance of Palaeogyrinus 217 
published, but under the circumstances I shall refrain from 
a discussion and shall be content with pointing out certain 
facts which seem thus far to have escaped notice, and which 
at once reduce the matter to its simplest elements. 
To return to the most important character, the structure 
of the middle legs, a glance at von SchlechtendaFs figure 
will show that, in spite of the huge tarsi, comparable in 
their development with the swimming feet of such powerful 
divers as Laccophilus and Cybister, the femora are slender, 
and the coxae drawn so small that the whole leg is gro- 
tesquely disproportioned. Furthermore, the posterior legs 
have powerful femora hinged to broad coxal plates, but 
have no recognizable tarsi, though we should expect to find 
heavy ones attached to such bases. Now if tibiae should be 
drawn between the hind femora and the so-called middle 
tarsi, a pair of well-proportioned swimming legs would be 
formed in a position in which they are found in a good 
percentage of recently killed dytiscids today, and we should 
have to assume the loss of the imprints of only the typically 
slender mesotarsi, which might actually be covered by those 
of the heavy hind legs. Thus by a small change, and re- 
ference to the original figure will show how slight it would 
need to be, we should replace an anomalous and unconvinc- 
ing insect by a nearly typical dytiscid, such as might well 
have occurred in the geological period in question. Any 
doubt that this suggested reconstruction is the correct one 
in spite of the original figure is, I think, removed by von 
Schlechtendal’s own statement that the different parts of 
the posterior legs cannot be surely recognized, since they 
have left only slight impressions. 
Among the characters of secondary importance, the 
entire eyes indicate at once the dytiscid affinities of the in- 
sect, as do the rest of the discernible structures except, 
perhaps, the mesosternum. As the latter is figured it is 
larger than in the Dytiscidae, but if, as we may suspect, the 
suture between it and the metasternum is imagined or due 
to a crack in the rock, we should avoid even this difficulty, 
for an anterior projection of the metasternum would meet 
the intercoxal process of the prosternum, the typical 
