witter: unio luteolus and its allied forms. 175 



(B), from the Cedar river, in Muscatine County, weighs 14 02., 

 length 14.8, width, 10.7, diameter 7.8 cm. 



It seems to me the luteolus, of Lamarck, is most likely, (a), 

 in group (A). It is a small light shell compared with the others. 

 (/?), of group (^y^j is known by some as siliquoideus of Barnes, but 

 Lea does not recognize this as a good species. The two forms 

 are not found in the same waters here, each occurring in several 

 localities in eastern and central Iowa, but in each case, so far as 

 I have seen the form is more or less closely maintained. \i sili- 

 quoideus cannot be retained as a species, it certainly is, in this re- 

 gion, a conspicuous variety. As to group (B), it is quite certain 

 some considerable misapprehension exists among conchologists- 

 It has been described under the name of ventricosus, by Barnes, 

 and figured as such in Say's Conchology. The form is abundant 

 in our interior streams, but not associated with group (A), so far_ 

 as I have seen. Some examples of group (B) vary tow^ards (a), in 

 group (A), and others are so close to occidens, as to make it diffi- 

 cult for me to separate them. Is it not probable that these three 

 forms are due to altered conditions under which they live? Most 

 of my correspondents send me form ( B ), labelled luteolus. It 

 would appear that luteolus varies in one direction towards ligainen- 

 tinus, Lamarck, of some of our streams, towards radiatus, Lamk., 

 &c., and in another towards canadensis, Lea, ventricosus, Barnes, 

 and cariosus, Say. There is a large group that seems to centre 

 about luteolus. 



Note on Helix rosacea, (Petterd). — Mr. W. F. Petterd 

 has described a Helix from Tasmania under the name o{ rosacea, 

 (J.C. vol. ii, p. 213) but that name is pre-occupied by Miiller, for 

 a South African species, now usually but not universally consid- 

 ered a variety oi H. globulus.— ]. S. Gibbons,M.B., Southampton. 



