HUDSON : Hogg's list of mollusca of stockton. 257 



Section I. — Univalve Shells. 



1. Nerita fluviatilis, Drap., Lin. Syst. — River nerite ; Don., 

 vol. i., tab. 16, fig. 2. Extremely rare in our rivulets. J. H. 

 has also found this shell at Seaton Shook and in the slake 

 near Hartlepool. 



[Neritina is scarcely likely to be native to the district, 

 but may possibly have been brought in with ballast. I 

 have never met with it. Dixon and Watson (" Land and 

 Freshwater Shells," Darlington, 1858), say, " We have 

 frequently obtained dead specimens from the ballast hills 

 near Middlesbrough, which have been brought from the 

 mouths of other rivers." — B. H.] 



2. Cyclostoma obtusum, Drap. ) Obtuse top shell. 

 Turbo fontinalis Lin. Trans. J Don., vol. iii., t. 102. 



Common in all the streams about Stockton. [This is 

 Valvata pzscinalis.\ 



[Page 24]. 



3. Cyclostoma impurum, Drap. ) Olive water shell. 

 Helix tentaculata, Lin. Syst. J Don., vol. iii., tab. 93. 



Avery abundant species. [This VaByihinia tentaculata.^ 



4. Planorbis- contortus, Drap. ) Thick, river cheese snail. 

 Helix concorta, Lin. Syst. J Don., vol. iii., t. 99. 



In the Billingham becks. [An erratum at the end of 

 the index reads : " P. 24, No. 4, for concorta read contorta.'"'\ 



5. Planorbis vortex, Drap. I Common whirl shell. 

 Helix vortex, Lin. Syst. J Don., vol. iii., t. 75. 



Exceedingly common. 



6. Planorbis marginatus, Drap.,t. 2, f 11,12 ) Marginated 

 Helix complanata, Lin. Syst. f whirl shell. 



In a ditch by the Osier Halt, near Norton Mill. 



7. Ancylus lacustris, Drap. ) Oblong fresh water limpet. 

 Patella oblonga, Lin. Syst. j Don., vol. v., t. 15. 



This shell is occasionally found in some of our rivulets. 



8. Ancylus fluviatilis, Drap. Ij^ Lake limpet. 

 Patella lacustris, Lin. Syst. j Don., vol. v., t. 147. 



J. H. has found this and the preceding species spar- 

 ingly in the mill race near Billingham Mill. 



