120 PARNID ZA. 
The genus Helichus, to which the New-world species of Dryops have hitherto been 
referred, was based by Erichsen on an error of observation, he having supposed that in 
Dryops the hind cox are approximate, while in /elichus he stated correctly that they 
are distant. Examination proves, however, that they are as widely separated in Dryops 
as in the latter genus; and as no other character has, so far as I am aware, been 
mentioned to separate the two supposed genera, and I quite fail to find any myself, I 
propose that the name Helichus should be reduced to a synonym. 
The genus Dryops consists of a single European and several N orth-American species, 
and includes also one from Java. ‘The New-world species are difficult to study, on 
account of their being generally covered with a stony incrustation deposited on them 
from the waters in which they live; they appear, moreover, to be very variable according | 
to locality, so that much difference of opinion is likely to prevail as to whether the 
forms found in different localities are specifically distinct. According to Dr. Horn these 
insects may be found in immense numbers; he states, indeed, /.c¢., that he has seen 
several hundred specimens on a stone not more than four inches square. It would be 
well for the North-American entomologists to make an examination of the amount of 
variation exhibited in some one locality; for such an investigation is necessary before 
we can know what to treat as “species” in a genus like Dryops. Only comparatively 
scanty material in this genus has been obtained from Mexico and the other portions of 
Central America; and feeling it to be unadvisable to propose new species in it without 
very good grounds, I have referred certain forms to North-American species, 
entertaining, however, no strong opinion as to whether or not they may ultimately 
prove to be distinct. 
1. Dryops productus. 
Helichus productus, Lec. Proc. Ac. Phil. 1852, p. 43’; Horn, Trans. Am. Ent. Soc. 1870, p. 82°. 
Hab. Norra America, California! and Arizona”; Mexico, Oaxaca (Hoge & Sallé), 
Guanajuato (Sallé). 
The series of about twenty individuals found by Hoge at Oaxaca shows scarcely any 
variation ; and I cannot detect amongst them any trace of the differences in the form of 
the thorax said by Horn? to be exhibited by the sexes. From other sources there are 
only three or four specimens ; and of these, two from Guanajuato form a well-marked 
variety of more elongate form, with more largely developed legs and diminished 
punctuation on the thorax. These two individuals approach more nearly to the 
Californian individuals in my collection than do the Oaxacan specimens; but they do 
not agree entirely therewith, though the differences are not of great importance. 
Whether these different forms are species, subspecies, or races, can only be determined 
by the examination of good series of specimens, aided by exact observations of lccality. 
M. Sallé had regarded the few individuals in his collection as representing three 
distinct species. 
