AQUATIC COLEOPTERA. 119 
4. Tropisternus platensis Reiche. Buenos Ayres, Santa 
Cruz. 
5. Cyclonotum globulosum Muls. Buenos Ayres, a single 
specimen. 
6. Berosus truncatipennis Cast. Castelnau’s description (Hist. 
nat. IT p. 56), applies pretty well to the male of a Berosus found in 
abundance by M. van Volxem at Santa Cruz, but there are also 
some other closely allied South American species to which it would 
be equally applicable; the females in these species have the sutural 
angle of the elytra, more acute than it is in the male. M. C. van 
Volxem also found in the same locality two other species of Bero- 
sus With the elytra not spined ; the species of the genus are nume- 
rous in South America, and as descriptions have been made by seve- 
ral authors without any common standard of comparison, it will 
be very difficult to make out to what: species these descriptions 
apply, until authentically named individuals can be procured for 
comparison. 
