1890.] NATURAL SCIENCES OF THILADELPHIA. 45 



The shells above described were at first refei'ed to the P. pelln- 

 cida of Pfr., or P. servUis Gld.; and later the writer gave to them 

 the mss. name of P. hordeacella. Whether the characters of the 

 form prove constant enough to give it specific rank, or whether it 

 will finally be considered a variety or race of P. servlUs Gould, is a 

 matter that my acquaintance with the group does not enable me to 

 decide. In its ccmstantly much smaller size we have a perfectly 

 tangible character that will enable one to readily sejiarate the two 

 forms without the use of a magnifier. 



In this connection it will be perhaps useful to point out the fact 

 that in the specimens sent out by Gabb as his Pnjm hordeacea there 

 are two forms mingled. One is the present species ; the other is the 

 true hordeacea, a form of about double the size of this, with a more 

 acute, stronger crest or ridge behind the outer lip, and a decidedly 

 pinched base to the last whorl. P hordeacea has the teeth of the 

 outer lip more deep-seated and smaller than P. servilis or P. hordea- 

 cella. 



The specimens before me are from the following sources : — Ari- 

 zona, collected by Dr. Horn ; New Braunfels and other places in 

 central Texas, collected by Mr. J. A. Singley and the writer; St. 

 Augustine, Florida, collected by Mr. C. W. Johnson, of the Wagner 

 Institute, Philadelphia. 



The figures on Plate I are drawn from New Braunfels specimens, 

 which may be regarded as typical for the species. 



