THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 237 
anterior end of each series appears usually to be (is?) formed by one 
of the pericornual nuclei. Sometimes these latter are the only ones to 
beseen. Almost always they are the largest. Starting anteriorly with 
these two, an increase may be traced up to 6 (3 on each side), the 3 
pairs being often subsymmetrically arranged. In cases of deficiency it 
is the posterior ones that are absent. These facts would seem to suggest 
a possible origin of the series from the two large pericornual nuclei. 
Besides the structures already described, others more or less similar 
may be seen, especially anteriorly and in the higher (presumably also 
in the lower) focus-planes. Some of these show the same combination 
(deeply stained granules in unstained areas) as those already men- 
tioned, but often no surrounding unstained areas were visible. 
Vacuole: I could not detect this structure, but do not wish, on the 
strength of the material available, to positively assert its absence. 
Habitat, etc.—Encysted immediately beneath the skin, on the external 
(scaleless) surface of the head, never elsewhere except twice in skin of 
body immediately behind head of Lrimyzon sucetta oblongus (= Catos- 
tomus tuberculatus Le Sueur, fide Jordan and Drayton’), chub sucker. 
Apparently a scaly surface constitutes an almost impassable barrier 
for this species. 
Observed on fish collected as follows: 
U.S. Nat. Mus. Cat. No. 20105. Tributaries Fox River, Mississippi. Collector, Prof, 
S.F. Baird. Tumors very numerous on 2 specimens. Fish adults. 
U.S. Nat. Mus. Cat. No. 20523. Kinston, North Carolina. J. W. Milner, collector. 
A single tumor on 1 fish; the latter rather young. 
This species was not found in the following: 
U.S. Nat. Mus. Cat. No. 20254. Near Piermont (?Pierpont) New York. Collector 
Prof.S.F. Baird. Fish half-grown. 
U.S. Nat. Mus. Cat. No. 25573. Columbia, South Carolina, March 21,1880. Col- 
lector, Col. Marshall McDonald. 
The striking contrasts between the very great number of cysts present 
on the fish from Mississippi and their extreme rarity upon those found 
at the other localities is interesting. Dataare, however, wanting for the 
proper appreciation of relative potency of geographic location, tempera- 
ture, season, and age of the fish. 
Remarks.—This species is, I believe, identical with the one described 
by Miiller.* Although he states the branchiz to be the principal seat 
of this species, I have only found it imbedded under the skin covering 
thehead. The cysts found on the branchie, besides being distinguished 
1J have not seen more than 3 nucleiform bodies (deep-stained granules in the 
midst of a non-stained area) on a side, though the number of deep-stained granules 
may be greater, 2 being sometimes found in one unstained space. 
2 Bull. 12, U.S. Nat. Mus., pp. 100, 145; var. oblongus, fide Prof. B. W. Evermann. 
3Miiller’s description in brief is: 
Cysts conspicuous, elongate, 2 to4 mm. long, imbedded principally under mucous 
membrane of branchial lamellz, also in that of the branchial chamber and in skin of 
head of Catostomus tuberculatus from North American rivers. Cysts found in all of 
the 3 fish examined, being in one case numerous, 
