172 Quarterly Journal of Conchology. 



for without doubt, links exist connecting the extreme forms, and in 

 determining a species we have to examine correlative forms wide- 

 s pread over a geographical region. 



Dr. Jeffreys' remarks about the Pisidia-''%\zt, substance, sculpture 

 and lustre are not of much account" — without doubt apply only to 

 that genus, and are used touching the determination of a species- 

 Thus we have P. fo7itinale and its four varieties varying much in all 

 these qualifications, yet they all belong to one species; at least this 

 is the opinion of a master of the science who has examined "thou- 

 sands of specimens" collected from all parts of Europe. 



Next the Zonites — all our species are well marked and I cannot 

 admit that the distinctions between any of them are "very trifling." 

 The two approaching nearest to each other are Z. alliarius and Z. 

 glaber, but the latter is much the largest and has a smaller umbilicus 

 than alliarius, this latter character being very striking in continental 

 specimens which I have examiiied. Z. purus and Z. radiatulus are 

 certainly very distinct and preserve their character, although often 

 occurring together, and we cannot dispute the identity of a species 

 because " the lens " is a necessary vehicle to its proper examination, 

 or we might as well dispute the distinctness of all microscopic 

 organisms of infinitely greater difficulty of examination. 



Helix nemoralis and H. hortensis, although occurring together, * 

 are not considered by Dr. Jeffreys to be distinct, or, as w^e might 

 put it. Helix nemoralis is found in company with another form — 

 H. hortensis, with which it is connected by the variety hybrida, i. e., 

 not preserving its distinctive character, but intermingling with 

 hortensis and producing intermediate forms ; on the other hand, if 

 the two forms never occurred together they would have to be regard- 

 ed with suspicion, being so nearly alike, as constituting a species 

 and variety; and it is this reasoning Dr. Jeffreys applies to the var. 

 oi Limncea palustris (p. i i4)-as it occurred alone it was to be regard- 

 ed as a local variety, whereas, had it occurred with other forms and 

 still maintained its character without intermingling, it would have 

 had some claim to specific distinction. Of course this is a rule to be 



* Dr. Jeffreys is certainly aware of the fact of the two forms occurring together 

 and mentions the circumstance in the 5th volume of his excellent work. 



