1968] 
Chickering — Genus Ischnothyreus 
81 
distal end sharply pointed and strongly chitinized; apparently also 
accompanied by a soft, median portion. Lip much wider than long; 
sternal suture procurved. Sternum : convex ; smooth, without grooves 
as in Dysderina; with a sparse supply of stiff bristles; about as wide 
as long ; bluntly terminated between fourth coxae which are separated 
by nearly 1.6 times their width. Chelicerae: nearly vertical; parallel; 
moderately robust; fang long, slender and curiously knobbed at base 
(Fig. 2) ; fang groove without definite teeth but some specimens 
may have a small number of very minute denticles. Legs: 4123 
in order of length; tibial index of first leg 12, of fourth leg 8; spines 
essentially as recorded by Petrunkevitch (1929) and Bryant (1942) ; 
some variations have been noted among the many specimens now 
available for comparison. Palp: quite unlike Figure 264 (Simon, 
1893) which may have been taken from a specimen of Opopaea ; 
essentials as shown in Figures 6-8 : all segments simple with no 
special modifications except tarsus; all segments strongly chitinized 
and dark brown. Abdomen : ovoid ; with dorsal scutum as shown 
in Figure 4; division between epigastric and ventral scuta quite in- 
definite but genital aperture shows clearly near the center of this 
region. Color in alcohol: carapace yellowish in a broad central 
region, grayish along lateral regions from opposite palps to lower 
part of posterior declivity; two oval darker areas dorsolateral in 
position in anterior portion apparently because of colored internal 
parts (I. omus Suman, 1965, Fig. 1). Sternum and legs yellowish 
with some variation. Palp: all segments from trochanter a dark 
brown. Abdomen : dorsal scutum light brownish ; ventral and epi- 
gastric scuta yellowish, only slightly darker than regions not covered 
by scuta. 
Female. Total length 2.21 mm, including extended spinnerets 
(Simon gave length of female holotvpe as 3.5 mm). Carapace .76 mm 
long; .64 mm wide; about .22 mm tall. Dorsal abdominal scutum 
small, reaching somewhat less than half way from base to posterior 
end of abdomen (Fig. 9) ; epigastric and ventral scuta essentially as 
represented in Figure 10; some variations in appearance of scuta have 
been noted among the many specimens now available for study. Dr. 
Petrunkevitch’s description of the female from Puerto Rico (1929) 
may be consulted for more detail; he stated, however, in his key to 
the Oonopidae of Puerto Rico that the female had no ventral scuta. 
Records. Several dozens of specimens were taken at Turrialba, 
Costa Rica, July 25-August 15, 1965. Hundreds of both sexes are 
in my collection from numerous localities in the Panama Canal Zone 
and Panama proper taken during the past fifteen years. More than 
