NOTES ON CEYLONESE TETRIGIN 
141 
that the whole country was in a state of drought, and also from the 
fact that he found certain Tettigids (which I determined to be 
Systolederus anomalus) burrowing under dry moss on a rock. 
The behaviour of Tettigids under changing climatic conditions, 
such as moisture and dryness, is one of great importance from 
the evolution standpoint, and further data are needed. The segre¬ 
gation of certain species under one condition of dryness, and their 
dispersal under another condition of moisture, forms a theme worthy 
of further study, if nothing more were gained than the light it 
might throw on the subject of isolation and natural selection in 
this group. 
Scelimena gavialis, Saussure. 
Ann. Soc. Entom., France, p. 485, 1860. Figured by Hancock in 
Spolia Zeylanica, vol. II., Plate I., figs. 4-4c. 
This is one of the most interesting aquatic species found in Ceylon. 
Its hind tibiae are modified into perfect paddles for swimming. 
This species is often found on dark coloured rocks projecting above 
the water in the streams, and readily jumps into the water when 
disturbed. It frequently submerges its body completely, and 
clings to the stones on the bottom. But finally, when the supposed 
danger has passed, it crawls up again on to the rocks. Mr. Fletcher’s 
first captures of this species were at Haputale (4,800 feet) in the 
Province of Uva on September 18, 1907, under which date he writes : 
“ The first specimen taken was found in the net when catching 
Notonectids in a small stream ; the second was seen swimming under 
water against the current with its wings closed ; it settled on a stone 
under water, and looked not unlike a dragon fly larva. Subsequently 
about a dozen were taken sitting on rocks near little cascades. 
They seemed to be gregarious and inclined to be social, for they 
occurred in little groups of about half a dozen specimens in a space 
of a few yards, and on several occasions two specimens were seen 
sitting side by side on a rock ; in at least two instances these proved 
to be male and female. In spite of the vivid red edging to the 
thorax, this species is not at all conspicuous on the dark rocks 
on which it rests.” Under date December 19, 1907, Mr. Fletcher 
notes two examples taken along a stream on Cocogalla estate (4,000 
feet) in the Madulsima district : “ These two, apparently male and 
female, were at rest on the same rock, but two or three inches apart. 
They usually seem to go in pairs, male and female, but I have not 
seen them in cop .” Mr. Fletcher also says : “ At Madulsima, May 
13, 1908, a small rocky-bedded stream contained some immature 
Metrocoris stall , and on the rocks were numerous examples of 
Scelimena gavialis . As usual, these were generally sitting on the 
rocks in pairs, close to one another, near the surface of the water, 
but I saw none in copulation. On being disturbed they jumped into 
the water and clung to the stones on the bottom, crawling up again 
