358 Irving » Variations in Teeth of Whelk. 
in books by pen-and-ink drawings not always true to life. A 
central set of five, six, or seven, small uniform ‘ V’s’ hanging 
from a straight line separated by blank spaces from lateral 
plates bearing three, rarely four, tusks, may furnish a general 
idea of the palatal arrangement sufficient for identification, 
but features of some importance are lost through absence of 
detail. Two photo-micrographs, one sharply focussed on 
smaller central teeth, and another on larger lateral tusks, are 
reproduced ; they do not quite tally with the printed sketches 
referred to. Whelks are carnivorous animals capable of boring 
through shells of other molluscs. Their teeth correspond to 
their needs, and are structurally diverse from those of vegetable 
feeders. The ‘ centrals,’ more or less round tapering to sharp 
points, are very seldom strictly uniform. Counting from left 
to right, teeth pointing downwards, the first and fifth in each 
transverse row are practically alike and about twice as broad 
as the slender third. The fourth, slightly bevelled at its tip, is 
longer than the third, while the second, distinctly and abnor- 
mally bifurcated, bears some resemblance to fangs of human 
teeth. This forked condition cannot be considered as partial 
fusion of two teeth seeing this second tooth arises from a single 
socket. All five teeth seem to be firmly fixed in five clearly- 
defined deep sockets, and not merely surface-set on a plate. 
Such an alveolar implantation, combined with a small degree 
of curvature makes for rigidity and strength. A curious and 
most interesting circumstance is the marvellous faithfulness 
with which all the peculiarities of any one transverse row are 
repeated in every other row, distant or near—a proof, if need 
be, that the entire series develops, in sequence, from one and 
the same moulding source providing and pushing forward a 
continuous supply to replace inevitable loss caused by tear 
and wear in front. Though the group of central teeth is 
obviously placed away from the ‘ laterals,’ yet no blanks are 
manifest in the photo-micrograph, for each socket-plate bridges, 
on both sides, the distance between, and is apparently attached 
to the longitudinal ligaments which connect the outer teeth. 
These conspicuous side teeth are remarkable for size, position, 
and character. Angled and sculptured for efficiency and 
_resistance, it is open to any microscopist to regard each massive 
plate either as one tooth or four. Four fang-like processes 
certainly spring from a solitary base, but as base and processes 
together constitute one unjointed piece a natural conclusion 
is that as a whole it acts as one tooth. Probably the straight 
innermost projection serves as a pivot during circular excursions 
of the great external tusk while the two lesser fangs, as supports, 
insure steady rhythmic working. At any rate the pivot may 
be a clue to one function in which the tooth is used as a shell- 
perforating tool. 
Naturalist, 
