30 THE NAUTILUS. 



The shell is differentiated from U. coruscus hy being smaller ; hy 

 its parallel outline ; by its posterior point being lower and more 

 biangular. In proportion to size, it is heavier in texture, and when 

 perfect shells of both are compared, it is not so shining as is coruscus. 

 The squarely built anterior end is a character common to a number 

 of Florida Uniones. 



The habitat is Reedy Lake, Polk Co., Florida, in the Gulf 

 drainage. Specimens in cabinets of Mr. Bryant Walker, of the 

 Academy of Natural Sciences of Philadelphia, and in my own. 



A plate illustrating the type of U. coruscus Gld. and this species 

 will appear in the next number. 



NOTE ON THAIS (PURPITRA). 



BY MRS. M. BURTON WILLIAMSON. 



Having recently received a fine series of American Thais or Pur- 

 pura from Mr. Henry Hemphill, the well-known student of variation 

 in shells, it occurred to me that his notes on these shells would be of 

 interest to the readers of the Nautilus. The shells, comprising 

 over fifty varieties of form, sculpturing, color, etc., were collected by 

 Mr. Hemphill on the coast of Maine, Puget Sound, "Washington, 

 Oregon and California. 



As the earlier readers of the Nautilus are aware, Mr. Hemphill 

 takes one species as the type of a group, and around this type he 

 places other species as types of varieties. 



Many years ago P. P. Carpenter and George W. Tryon ' noted 

 the strong resemblance between Purpura lapillus L. of the eastern 

 coast of North America, and P. saxicola Val. of the Pacific shore. 

 Mr. Hemphill, while agreeing with them, would group our west 

 coast species around P. lapillus L. as the progenitor of the whole 

 series. He compares shells he collected on the coast of Maine with 

 P. saxicola of the west coast, and a tray of these shells are, as he 

 says, " almost ident'cal in every respect with Tomales Bay, Cali- 

 fornia, specimens." These selected specimens are puzzling indeed 

 when we consider the geographical area from which they were 

 collected. 



1 Manual of Conchology, Vol. II. 



