NELSON AND TAYLOR : ON YORKSHIRE MOLLUSCA. 7 



Class CONCHIFEHA. 



Order LAMELLIBRANCHIx\TA. 



Family SPH.FRIID.F. 



Genus S P H .-E R I U M , Scopoli. 



A group of widely diffused bivalves, whose metropolis ap- 

 pear to be in the Western Hemisphere. 



There are four British species, all of which are found within 

 the limits of our county, inhabiting ponds or canals, though 

 occasionally met with in quickly running streams. 



Mr. Temple Prime, in his 'Monograph of the American 

 Corbiculadae,' proposed an arrangement of SplKznuin which would 

 separate our British species into two distinct genera having as 

 their types Z. corneiiiii, S., and S. lacustre, Miill. 



As will be seen, we have reduced to the rank of synonyms 

 several shells described as distinct by American authors, two at 

 least of which, ^. ovale. Fer., and S. Fisidioides, Gray, are now 

 pretty generally allowed to have been introduced from the New 

 World. 



It is to be regretted that in the county we have no special 

 student of this and the allied groups, which may account for the 

 comparative paucity of the records, our own attention being more 

 specially directed to the Pulmonifera. 



Sph^rium corneum, (L.) 



Sphasrium Vermontanum, Prime. 



Lovell Reeve, in his ' British Land and Freshwater Shells,' 

 says this species is closely represented in the United States by Say's 

 C. partumeia ; this is however erroneous, S. partumeitim, Say, 

 being synonymous with S. laciistre, Miill, as shown hereafter. 



It is however closely allied to, if not identical with, S. rhom- 

 boideum, Say, as pointed out by Dr. Jeffreys, in his ' Comparison 

 of the MoUusca of Europe and Eastern North America.', 



