OF CONCHOLOGY. 
35 
The rhachidian tooth is broad, rounded before, and with thè 
base arcuate behind. The cusp is siraple, rounded before, and 
more or less pointed behind. In some individuals this point is 
more prolonged than in others, and in such cases thè tip is trans- 
parent, while thè rest of thè cusp is yellowish. The inner 
twenty-seven laterale bave a longitudinally arcuated rhomboidal 
base, of which thè anterior edge is produced before thè cusp. 
The lattei’ is long, with one prominent long denticle, and one 
short and triangolar on thè inner side. The tips of these den- 
ticles are more or less transparent, while thè body of thè cusp 
is yellow, and thè thick base showing through is liable to mislead 
thè observer, as to thè form of thè cusp. The twenty-eighth 
luterai is similar but broader, with a shorter denticle, more or 
less bifid or arcuate at thè tip, and thè cusp is broadly rounded 
on thè outer side. The twenty-ninth has thè prominent denticle 
emarginate, broad and rounded, and has a third denticle on thè 
outer side. The emargination of thè chief denticle is more ob- 
vious in young specimens, and in old ones is not always notice- 
able, except in a smaller nuraber of thè laterale. The laterale 
gradually increase in width and decrease in length toward thè 
edge of thè radula, and in thè extreme outer teeth bave thè three 
denticles rounded, sub-equal, and thè base more than twice as 
wide as it is long. 
The cusps of thè inner laterale are, to a certain extent, bayo- 
net-shaped, as will be seen by thè figure. There are about two 
hundred and fifty rows. 
Muscular System. There are no internai bande of muscular 
fibre as in Melampus or Gadinia. The muscles which control 
thè bùccal mass are not strongly developed. The muscles of 
thè preputium are spirally arranged in two layers. 
The adductor is divided into three parte. On thè right a 
broad passage exists where thè opening of thè pulmonary cavity 
lies. The small portion of thè right limb of thè adductor, an- 
terior to this, is rounded-triangular. The mantle is attached to 
thè shell, over thè head, so that thè scar is continuous. The 
l’ight extremity of thè posterior part of thè adductor is broadly 
rounded. On thè left thè scar appears continuous, but thè an- 
terior and posterior parte, though approximate, are separated 
by a suture, showing a tendency to bilateral symmetry. The 
left anterior portion closely approaches thè buccal mass. 
The foot is moderately thick and muscular, and divided by a 
very faint median line in its internai muscular structure. The 
nerves and blood vessels.mostly enter thè foot in this line. 
Circulatory System. The heart is enclosed in a sac, of which 
