Rotatoria E 5 



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) hofsteni 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 360 M ; toes, 22 U ; trophi, 52 M . 



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 BRAGHIONID^:. 

 Platyias quadricornis (Ehrenberg). 



Nbteus quadricornis HUDSON and GOSSE, Rotifera, 1886, vol. 2, p. 121. 

 pi. 28, fig. 5. 



A few specimens occurred in a collection from lakes on Old Crow river 

 flats, 80 miles north of New Rampart House, visited by Jessup on July 11, 1911. 



Keratella quadrata (Muller). 



Anuraea aculeata HUDSON and GOSSE, Rotifera, 1886, vol. 2, p. 123, pi. 29 

 % 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 HUDSON and GOSSE, Rotifera, 1886, vol. 2, p. 124, pi. 

 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 (Muller). 



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 



240582 



