214 PECTINIBRANCHIATA.—DENTALIADA. 
still more sedentary than the true Limpets, for 
there may be seen in certain individuals of the 
P. Hungaricus irregularities, proceeding from the 
body on which it has lived when young, continu- 
ing exactly the same to adult age; irregularities 
whose traces may be observed on the lines of 
growth, and which prove, in the opinion of M. 
Deshayes, that during its whole life the animal 
has never changed its place. But, probably, M. 
Deshayes was not aware of those interesting facts 
which have been observed in the habits of the 
true Limpets, already described in these pages; 
for, if a similar habit of roaming for food, and 
returning with precision to the exact spot which 
it has chosen as its home, be common to the Fools- 
caps also, it appears to me that the phenomena 
alluded to by the eminent French zoologist would 
be siafficiently accounted for without his hypo- 
thesis. 
FAMILY DENTALIADA. 
(Tusk-shells.) 
On many a pebbly beach upon our coasts there 
is frequently found, among other shells washed up 
by the sea, one which bears the closest resemblance 
to an elephant’s tusk in miniature. It is the re- 
presentative of a family, comprising but a single 
genus, which is interesting because rts characters, 
as well those of the shell as of the animal, manifest 
a decided approach to those of another great divi- 
sion of organized beings, the ARTICULATA. Indeed 
it was formerly considered by the best zoologists 
to be a genus of Annelida, allied to those which 
form the shelly tubes so commonly seen on sub- 
