For a number of years, a line has been drawn between animals which merely live in water but obtain atmospheric air for respiration, and those truly aquatic forms which depend upon oxygen removed from solution in the water surrounding them. In making a study of the latter type of organisms, we recently noted that there are two distinct methods of respiration correlated with rate of blood circulation.

The genus Fabriciella, as considered by Tothill (Can. Ent., LVI, 1924:257-269) and Rowe (Ann. Ent. Soc. Am., XXIV, 1931 : 643-678), includes twenty-eight nearctic species. On the whole, the species are quite similar in general appearance, but in most cases readily separated, in the male sex at least, by genitalic characters.

I am indebted to the Connecticut Geological and Natural History Survey through Dr. W. E. Britton, its Superintendent, for the facilities which make this study possible. I wish to thank Miss E. B. Bryant of the Museum of Comparative Zoology and Dr. W. J. Gertsch of the American Museum of Natural History for allowing access to material in their respective collections as well as for kind aid and advice.