36 IOWA STUDIES IN NATURAL HISTORY 
Family Mesoveliide 
Microvelia (?) pulchella Westw. 
One apterous specimen, Barbados, May 21, 1918, Stoner. 
This is the Westwoodian species type of the genus, so far as 
it is possible to determine from a single apterous specimen. 
Here is another group in which color has been much used as a 
specific character. In Microvelia, my esteemed contemporaries 
to the contrary notwithstanding, the only characters for dis- 
tinguishing surely the winged and wingless forms are the head 
and its appendages, the legs, and the genitalia. The genus is 
certainly dimorphic; perhaps even polymorphic. It is a truism 
of taxonomy that the presence or absence of wings modifies pro- 
foundly the structure of the thorax, that portion of the body 
which contains and serves as anchorage to the alar muscles. 
Wing conditions per se, and therefore thoracic size and struc- 
ture, cannot be used as specific characters to fix a species in all 
its forms. We must of necessity lay stress on the unchanging 
structures named above. For this reason, no specific deserip- 
tion of any waterstrider for one form only may be considered 
adequate; and no description which does not lay stress on the 
unvarying structure is complete. The description may be ex- 
cellent for one or another form, but useless for the undescribed 
one in the absence of the required universal characters. 
Family Mesoveliide 
Mesovelia sp. 
One specimen, Antigua, June 28, 1918. Stoner. This speci- 
men is in fair condition only. It is neither our Eastern United 
States bistgnata Uhler, nor the smaller Antillean M. amena 
Uhler. It may be mulsanti B. White, but this is a mere guess. 
Notwithstanding Horvath’s 1915 monograph, the group con- 
tinues in unsatisfactory condition. As may be noted, I still 
employ Uhler’s name bisignata for our Eastern species, in the 
face of Champion’s dictum in Biologia Centrali Americana. The 
species of Mesovelia are readily separable, but here again my 
preceding remarks apply. Horvath, to be sure, has drawn at- 
tention to two processes on the male genital plate, yet these 
alone are insufficient, for I have been able to separate by good 
characters Kirkaldy’s M. orientalis from Horvath’s vittigera, 
