Marine Shells of Massachusetts. 271 
The operculum is horny, lamellar, elliptical ; the 
strie of growth very large; stages of growth very evi- 
dent; the older portion sometimes appearing to be 
merely glued upon the upper extremity and outer sur- 
face of a new operculum ; around the margins of the 
surface of attachment, it is covered with a shining, wax- 
colored deposit. 
In the P. cárica the rondi ving series of iubeseles marks 
the periodical stages of growth, which do not appear in 
the P. canaliculdta. From each tubercle downward, a 
former labrum, although not reflected, is conspicuous 
on specimens whose surface has not been eroded. 
In my cabinet is a specimen, which may be regarded 
as a well marked variety. In the progress of growth, 
each successive whorl is usually placed upon the pre- - 
ceding as high up as the series of tubercles, so that, as | 
Lamarck observes; the tubercles on the upper whorls 
are at their base. But in this individual, which was 
found last year, living, in the harbor of Nantucket, the 
successive whorls are applied below the tubercles, at a 
distance which increases in receding from the apex, and 
which measures one third of an inch at the labrum. 
The columella also is less arcuate, and the cauda 
straighter than in the common P. carica, and the aper- 
ture is less, The colors are also unusual. The lower 
portion of the columella, and upper and lower in ler Sur 
face of the labrum, are white; the middle of the labr 
is tinged, not very deeply, with a dull red purple. The 
inner surface of the labrum of the penultimate stage of 
growth is yellowish brown, irregularly tinged with deep 
brown. On and near the labrum, the labra of former 
stages of growth are very conspicuous, and are colored 
