Dakin and Latarche — The PlanMon of Lough Neagh. 57 



lu the Scottish lakes Murray and PuUar state Anurea acvdeata is only of 

 rare occurrence, and then only in the smaller lakes. This species with 

 A. cochlearis belongs to the cosmopolitan community of Wesenberg Lund. 



Kofoid records the species from the waters of the Illinois Eiver, where 



it appeared in March, 1898, and increased to a maximum in May. It then 



declined and disappeared in June. There were, however, scattered occurrences 



throughout the winter months, and in 1894 Kofoid records an autumnal pulse 



in September. 



Polyarthra. 



Folyarthra platyiotera Ehr. — Occurs in Lough Neagh in fairly large 



numbers. Except for A. cochlearis, it is the most frequent of the Rotifers. It 



appears towards the end of May, and increases rapidly until it reaches its 



maximum in August and September (51,000 in the combined catches). It 



disappears completely in January, and is absent throughout the winter and 



spring months. Murray and Pullar record P. 'platyp,e,ra, as genei'al in the 



Scottish lochs and in the rest of Europe. Wesenberg Lund states that in 



the larger Danish lakes the species is dicyclic, the sexual period occurring 



during March and April being the most marked. This differs strikingly from 



the state of things found in Lough Neagh, as here P. platyptera is absent 



altogether from the plankton until late in May. In the ponds in Denmark 



the species is polycyclic. In the Baltic lakes Apstein records P. platyptera 



from the Dobersdorfer See, where it is present in all the months except 



March. It reaches its maximum in July to August. In the Ploner See it is 



present throughout the year, and reaches its maximum in May. P. platyptera 



is included in Wesenberg Lund's list of the cosmopolitan species of Eotifers. 



P. platyptera is recorded by Kofoid from the waters of the Illinois, where it is 



one of the most abundant of the Eotifera. It is perennial ; but during the 



colder months, October-April, it occurs only in small numbers. It attains its 



maximum in April ; but it is polycyclic and has monthly recurring pulses. In 



addition to the widespread distribution of Polyarthra indicated above, it may 



be added that the species has been sometimes found to occur in the brackish 



water of the Baltic. 



Ifotholca. 



Notholca Imigispina Kell. is another Kotifer of widespread distribution, 

 and belongs to the cosmopolitan plankton community of Wesenberg Lund. 

 The long spines present in this species are probably, like many other long 

 processes developed in active plankton organisms, for giving stability in 

 movement — orientating organs — and not organs for buoyancy. 



The species occurs in the plankton of Lough Neagh in small numbers ; but 

 it seems to be present throughout the year. It is not recorded for November 



