1963 ] 
Y oung — Hydrovatus 
185 
The relationship between pustulatus and compressus is still not 
completely determined, but the two apparently represent the extremes 
of a single species which varies geographically. Typical pustulatus 
decreases in size from north to south and possibly also to the east 
in North and South Carolina and Georgia. The largest specimens I 
have seen are from Wisconsin, Michigan, New York, Illinois, and 
Indiana. Specimens from Virginia, Tennessee, Arkansas, and northern 
Louisiana are smaller although very similar in other respects. Speci- 
mens from Cherokee County, Alabama; Mitchell, Lanier, Baker, and 
Decatur counties, Georgia; Houston County, Alabama; and Calhoun, 
Jackson, and Walton counties, Florida, apparently represent inter- 
grades between typical pustulatus and the smaller, darker compressus. 
The latter apparently replaces pustulatus in the Atlantic and Gulf 
Coastal plain from Louisiana to North Carolina, although occasional 
specimens occur which have when teneral elytral markings of the type 
of pustulatus. 
The male genitalia (fig. 3) 2 of the single type of compressus (in 
BMNH) is as far as I can see identical with those of pustulatus 
(fig. 2) and with those of numerous specimens examined from 
throughout the range. Specimens from southern Florida tend to be 
smaller and somewhat more coarsely punctate than the type of com- 
pressus , but in other respects agree with it perfectly. Specimens from 
North Carolina (Brunswick Co., Near Bishop, vii.25.1959, F.N. 
Young in University of Michigan Museum of Zoology) and South 
Carolina (Beaufort Co., Cambahee River marsh, vii.25.1959, F.N. 
Young in UMMZ) although variable are also very similar to the type 
of compressus. I have also seen a single female from the Bahamas (San 
Salvador Island, near Cockburn Town, iii.18.1953, E. B. Hayden in 
American Museum of Natural History) which probably also repre- 
sents compressus. 
Hydrovatus inexpectatus new species 
Diagnosis: A small, pale Hydrovatus (fig. 4) similar in shape to the 
Brazilian crassulus Sharp (fig. 6), but differing from that species in 
the smaller size (1.89-2.15 mm in length) and the different structure 
of the clypeus. Body form less convex than any of the American 
species and with the sides of the elytra converging so gradually that 
they appear almost parallel-sided when viewed from above. Male 
2 The genitalia of the type were unfortunately lost after the above figures 
were drawn. A specimen from Florida with genitalia intact and previously 
compared with those of the type has been deposited in the BMNH. 
