Rotatoria BS 
manubria are long and strongly curved, so that their posterior ends meet in the 
median line. The bar intervening between the uncus and manubrium is prob- 
ably only a local sclerification of the walls of the mastax, developed in response 
to a specialization of the typical forcipate trophi. A very similar structure 
is found in Encentrum ricciae Harring; comparison may be made with Encen- 
trum (=Diglena) hofstent de Beauchamp, which shows a simpler stage of the 
same development. The unci and the supplementary piece are no doubt 
closely joined to the rami, the several pieces moving together virtually as a 
unit. 
The oesophagus is long and slender. The gastric glands are elongate 
oval and fairly large; they open into the stomach very close to the junction 
with the oesophagus. There is no constriction between the stomach and 
intestine. The ovary is fairly large and of somewhat irregular outline. A 
small bladder is present. The foot glands are pyriform and rather small; no 
mucus reservoir is present. 
The ganglion is elongate saccate; no retrocerebral organ or eyespots are 
present. 
Total length 360u; toes, 22"; trophi, 52u. 
This species was found in abundance in a collection made by Johansen 
among algae in a brackish lagoon west of Martin point, on the arctic shore of 
Alaska, on July 28, 1914. 
FAMILY BRACHIONID~. 
Platyias quadricornis (Ehrenberg). 
Noteus quadricornis Hupson and Gossz, Rotifera, 1886, vol. 2, p. 121, 
pl. 28, fig. 5. 
A few specimens occurred in a collection from lakes on Old Crow river 
fluts, 60 miles north of New Rampart House, visited by Jessup on July 11, 1911. 
Keratella quadrata (Miiller). 
Anuraea aculeata Hupson and Gosss, Rotifera, 1886, vol. 2, p. 128, pl. 29 
fig. 4. 
- This species is widely distributed in the Arctic; it was found in the follow- 
ing localities: among algae in a brackish lagoon west of Martin point, arctic 
Alaska, July 28, 1914; in freshwater plankton from the lake south of Bernard 
harbour, November 28, 1915; May 6 and 7, May 21, and June 12, 1916; all 
collections were made by Johansen. In Jessup’s material it occurred in a 
small pool near the International Boundary line, lat. 69° 20’ N., long. 141° W., 
July 23, 1912, and in a slough of Old Crow river, near New Rampart House. 
Keratella cochlearis (Gosse). 
Anuraea cochlearis Hupson and Gosssz, Rotifera, 1886, vol. 2, p. 124, pl. 
29, fig. 7. 
Not common in the Arctic; a few specimens were collected by Johansen 
in the lake south of Bernard harbour, May 21 and June 12, 1916; by Jessup 
in a pool near the Boundary line, lat. 69° 20’ N., July 23, 1912, and in a slough 
of Old Crow river, near New Rampart House, August 7, 1912. 
Notholca striata (Miiller). 
This is the most abundant and widely distributed rotifer in the Arctic; 
it was collected by Johansen in a brackish lagoon at Martin point, Alaska, 
July 28, 1914; in the river-bed at Bernard harbour, August 16, 1915; ponds 
24058—2 
