THE NAUTILUS. 119 
which may be variable to a lesser or higher degree. It shows also that 
it is impossible to found a species upon one or even a number of' speci- 
mens from one locality with any degree of certainty. 
4. Beaks of Calyculina. The presence of ‘“calyculate” beaks 
and of caps on them, has been regarded as characteristic, first, for the 
type species (C. lacustris Miull.), and then for the genus. Both these 
characters had to be given up, as being not shown by all species 
(e. g. transversa) of the otherwise well-defined genus. As to the 
“caps,” they are by no means a constant feature of such species as C. 
partumeia, securis, etc., and during the last years numerous speci- 
mens were seen with the beaks simply rounded and having not even 
traces of caps. These caps are nothing else but the embryonic shell 
of the mussel, which is oblong or elliptic in perpendicular section, and 
the additional growth is formed at an angle asa tule. It seems that 
the specimens without caps were hatched during the warmer season, 
when the young may be expelled at an earlier stage of growth, while 
in cold weather they are retained longer in the brood pouches of the 
parent and there growmore convex. Numerous young have been seen 
with several narrow stripes, separated by lines of growth, along the 
edges of the valves. On the other hand, specimens of C. transversa 
are now and then seen with caps, and occasionally also Sphaeria and 
different species of Pisidia. This point deserves to be studied more 
. 
exactly. 
————_ + > > 
GENERAL NOTES. 
STATION OF LIMNA:A GRACILIS.—We have received from Mr. 
Bryant Walker the following note on the above species, extracted 
from a letter from Dr. R. J. Kirkland : 
‘¢ Perhaps you will be interested in an observation respecting 
Limneea gracilis Say. I think Dr. DeCamp was the only person 
who found it in Reed Lake, near this city (Detroit, Mich.), and 
he only found it one year in May. He once told me he collected 
eighty-five on the rushes, where ‘they had come to spawn.’ I have 
searched for it in the spring for the past three years, but have never 
found one. Last fall, as I wrote you, I found quite a number in 
November. ‘This fall, I found five on September 17, in the same 
place as last fall. A week later found eighteen, two weeks later 
found fifty. After that only two or three on each of several visits. I 
think it was because the community was exhausted. Have searched 
at other points in the lake, but unsuccessfully. They were found 
