16 THOMAS SAY FOUNDATION 
requires time and patience, and best results can be obtained only 
with freshly collected specimens. After the nymphs had been 
killed in weak alcohol they were placed in a tray containing a wax 
bottom to which the specimens could be fastened by means of 
small pins. Minutien Nadeln served very well for holding the ap- 
pendages in place after the nymph had been properly spread. The 
nymphs were then dehydrated in alcohol, and after they had 
been in 95% aleohol for several hours the entire specimens had 
hardened so that the pins could be removed without any further 
danger of distortion or of movement of appendages out of place. 
Each nymph was then placed in a clean petri dish, a piece of 
glass was laid on the nymph to hold it in place, and sufficient 
aleohol was poured into the dish to cover the specimen. To ob- 
tain a white background, the petri dish, containing the specimen, 
was placed on a glass plate underneath which a sheet of white 
paper was inserted about a quarter of an inch below the sur- 
face of the glass. For a black background, a piece of black velvet 
was fastened to the bottom of a tray. Fine pins were then used to 
hold the specimens up about a quarter of an inch above the 
velvet. After pouring enough alcohol into the tray to cover 
the specimen it was photographed. Artificial light was used in 
making all the photographs included in this paper. 
EXPLANATION OF TERMINOLOGY 
To facilitate the interpretation of the structures or characters 
which are referred to in the text and in the descriptions of the 
species, the following explanations are given (see also text figure 
De 
Length of body. This refers to mature nymphs, unless other- 
wise indicated, and includes the length as measured from the 
front of the head to the tip of the abdomen, exclusive of antennx 
and cerci. 
The terms long and short are unfortunate ones to use but in 
many instances it is almost impossible to express relative sizes 
and measurements in any other way; so these relative terms 
cannot convey full meaning until after one has become somewhat 
acquainted with the group. 
Form of body. The bodies of all the nymphs are somewhat 
flattened but the term ‘‘flattened,’’ as used here, refers to such 
forms as Acroneuria in which the body is very much depressed, 
while ‘‘eylindrie,’’ or ‘‘eylindrical,’’ denotes such forms as 
Pteronarcys, in which the body is only slightly depressed. 
