1 88 
Psyche 
[September 
differing from all the known American species in the flattened and 
widened intermediate antennal segments in the male (fig. n). Larger 
and less attenuate behind than pustulatus compressus Sharp with 
which it has usually been found associated ; smaller, more attenuate 
behind, and more finely punctate than peninsularis Young with which 
it was also associated. Male genitalia of same general type as in 
pustulatus but differing in shape of aedeagus and parameres. Al- 
though the antennal modification suggests some of the African species, 
the genitalia and other characters indicate relationship with the Ameri- 
can group. 
Holotype male: Body form broadly oval, less strongly attenuate 
behind than concolor; broadest at about basal third of elytra; dorsal 
profile convex, regularly curved ; ventral profile not strongly arched ; 
Explanation of Plate 19 
(Scale: 1 mm = approximately 10 mm on figure at X 10; 
approximately 34 mm at X 40; approximately 46 mm at X 60.) 
1. Hydrovatus cuspidatus Kunz., Corsica: Bastia, E. Reveliere (Sharp coll., 
BMNH). L-R. Ventral view of male aedeagus X 60; lateral view 
aedeagus X 60; inner face left paramere X 60; outer face right para- 
mere X 60. 
2. H. pustulatus pustulatus Melsh. Indiana: Monroe Co., Bloomington, 
x. 20. 1952, J. R. Munsee (UMMZ). L-R. Ventral view of male aedeagus 
X 60; lateral view of aedeagus X 40; outer face right paramere X 40. 
3. H. pustulatus compressus Sharp. Louisiana: New Orleans (male type in 
BMNH). Same as 2 
4. H. inexpectatus new species. Dorsal outline of holotype (UMMZ) X 10. 
5. H. inexpectatus new species. Holotype (UMMZ). As in 2 and 3. 
6. H. crassulus Sharp. Brazil. Dorsal outline of female cotype (BMNH) 
X 10. 
7. H. concolor Sharp. Mexico: Mexico City, Hoge. Male cotype (BMNH). 
L-R. Ventral view of aedeagus X 60; prosternal process X 40; lateral 
view of aedeagus X 60. 
8. H. platycornis new species. Holotype male (UMMZ). L-R. Ventral view 
of aedeagus X 60; prosternal process X 40; lateral view of aedeagus 
X 60 ; right paramere X 60. 
9. H. pustulatus compressus Sharp. Dorsal outline of male type (BMNH) 
X 10. 
10. H. pustulatus pustulatus Melsh. Dorsal outline of male (same as fig. 2) 
X 10. 
11. H. platycornis new species. Right antenna of holotype X 60. 
12. H. platycornis new species. Dorsal outline of holotype X 10. 
13. H. concolor Sharp. Same data as fig. 7. Holotype male (BMNH) X 10. 
Note: The male genitalia of Dytiscidae are retracted into the body on the 
side. In copulation they are extruded outward, rotated, and projected forward 
and downward. The parts in the above figures are designated in relation to 
the copulatory position. Dashed or cross-barred areas are easily distorted 
membranous portions or portions broken in dissection. The dashed line across 
the parameres represents the base of the sheath into which the genitalia are 
withdrawn into the body. 
