112 MAIACOZOA. GASTEROPODA. PULMOBRANCHIATA. 



extremely fragile, smooth, glossy; with the spire generally 

 short, the last turn very large ; the aperture oval, nar- 

 rowed behind ; the columella a li ttle twisted, the edge of 

 the outer lip thin. 



] . Physa fontindlis. Stream Bubble-Shell. 



Shell sinistrorse, oval, glossy, transparent, pale greenish- 

 grey ; with the spire very short, convex, and obtuse ; the turns 

 four, obsoletely striate, the first three extremely small, the last 

 ovate, ventricose ; the aperture ovato-oblong, very narrow and 

 acute behind ; the inner lip thickened, white. Length about 

 three-twelfths of an inch, breadth more than half the length. 



Physa fontinalis, as described by authors, varies considerably 

 in form, the length of tbe spire, the size of the aperture, and 

 other characters, in which respects it resembles [the species of 

 Limna?us, and affords materials for supposed species. The 

 individuals which I have seen, many thousands in number, 

 vary little from tbe above description. The spire is from a 

 fifth to a fourth of the whole length ; tbe breadth is greater or 

 less ; but the aperture is always about half tbe size of the 

 entire outline of the shell. The spire is always convex and 

 obtuse, sometimes eroded or trunculate. 



First found by me, while with my class, on an excursion to 

 tbe Loch of] Skene, on tbe 2d of July, 1842. Having walked 

 all round, and partly through tbe lake, we found it everywhere 

 cast ashore or lying in patches at tbe bottom, in vast profusion, 

 intermixed with Cyclas flavescens. None of tbe individuals ex- 

 amined exceeded four-twelfths of an inch in length, or two and 

 a-balf in breadth. A specimen was found by Mr. Mitchell, 

 while searching with me, in a pool in the Dee, on the 16th 

 of July ; and on the 22d of August, I found one in the Don, 

 near Seaton. The last individual I kept alive for a fortnight. 



The following account of the habits of the species may prove 

 interesting : 



This animal, which is herbivorous, resides, with us, in lakes 

 and rivers, frequenting more especially beds of Potamogeton, 

 on the leaves of which it feeds. Its foot, when extended is 

 oblong, obtuse before, rather pointed behind; the neck of 

 moderate length, the fore part of the head obtuse ; the tenta- 

 cula long, tapering, very slender, almost sectaceous ; the eyes 

 situated at the inner base of the tentacula, and, being black, 

 very conspicuous, all the other parts being yellowish- white 

 and semitransparent ; the body oblong, spiral ; the mantle with 



