94 PROCEEDINGS OF THE CALIFORNIA 



during the winter hibernation or the low 'water of the dry season, and my ob- 

 servations confirm this, as all our forms without thig character when mature 

 inhabit waters never frozen nor dried up. Other waters, liable to dry up wholly 

 or in part, furnish specimens differing only in having the lip thickened. I there- 

 fore consider this as the normal condition, and its absence as merely. varietal, 

 when uncombined with other characters. Only the subfamily Ancijlinm is des- 

 titute of it in all cases. 



Dr. J. Lewis attributes the malleation of some species to rapid growth in 

 warm water, causing the shell to solidify unevenly ; and also mentions apparent 

 metamorphoses of one species into another quite different, merely from change 

 out of still canal water to that of a rapid brook. 



As to the first observation, I think that the forms called Limnop/i i/sa paliis- 

 tris, and elodes, often considered identical, and as having a circumboreal range, 

 at least as far north as Lat. 60°, sufficiently disprove it, for this malleation is 

 one of the chief characters distinguishing them from their more southern allies 

 L. umbrosa, Nuttalliana, etc. 



The second statement is so opposed to the testimony of all other observers 

 that it seems to me to require confirmation. 



Size, in connection with thickened lip and other marks of maturity, has been 

 made a specific character without good reason, for we find specimens, differing 

 in small size from larger types, confined to small springs, cold water, or tran- 

 sient pools, where the' want of nourishment is sufficient to stamp them as merely 

 dwarfed races. 



Color is another character often relied on as specific by those who study only 

 the dead shells. A few bleached specimens, picked up by an inexperienced col- 

 lector in a dried-up river bed, have been considered of natural color by even 

 the cautious and e.x^ct Dr. A. A. Gould, as when he named Phijsa virginea 

 from this very circumstance of " porcelain-like color," the living shell being 

 really of the usual amber-yellow of the thin species. 



Again : his Pkysa virgata was named from pale stripes alternating with the 

 usual hue, and the Ph. striata of Lea, as well as the Ph. sparsestriata Tryon, 

 were founded chiefly on the same character. In all cases, however, the speci- 

 mens came from waters either brackish from salt- mixture or from the alkalies 

 so common in the drier portions of this State, and appear to me merely acci- 

 dental varieties due to the introduction of the salts into the shell. 



I may add, that from my observation all the species are normally, when liv- 

 ing, of some shade of horn-color, varying from pale amber to dark brown, or 

 when opaque becoming black. Also, that all those of any one locality are 

 usually very similar in the color and thickness of their shells, the latter depend- 

 ing on the amount of lime in the water. This similarity extends to the colors 

 of the animals, for of the ten univalve species found in Mountain Lake all have 

 the same tint and thickness of the shell, and the same sipoky-black hue of the 

 animals, except an occasional spotted var. of Phijsa. 



In many places the shells are all incrusted with the black protoxide of iron, 

 and in others with the red sesquioxide. It is, therefore, useless to include color 

 as a specific character, although its variations may not always be so easily 

 explained. 



