2GS 
ECHIXOGLOSSATE TEETH. 
The uduiitophore of Tcstacelht haliotidea may be formulated as 
"¥^ + {} + S + |} + -r‘=xd8 = l,dG8, 
showing that there are 1,8G8 teeth arranged in 38 transverse rows, 
all of whicdi are dehcient of the middle and lateral series, but possess 
1 8 marginal teeth at each side, all of which are strongly barbed on 
one side of the apex like a fish-hook and may also he furnished with 
a sharp blade-like cutting edge on the convex side of the apex. The 
base of attachment ac(|uiros knobbed extremities, owing to the enlarge- 
ment of each end, for firmer attachment to the radnlar membrane. 
Typically the Beloglossate radnhn are deficient of a median row of 
teeth, although a minute mid-tooth may occasionally be met with in 
some part of the membrane. 
The Echinogloss.v (eyu'os', a hedgehog ; yAwo-o-a, tongue) may be 
an aberrant form of the Acanthoglossate teeth, with more numerous 
s])inons terminations and a more pronounced curve of the reflected 
liortion or more probably it may have ari.^en from a different stock, as 
the radical difference in the mode of convergence of the lateral trans- 
verse rows would seem to point to a different derivation. 
Fig. 5.‘^G. — Median portion of a transverse row of llie teeth of Physa fontinalis (L.) liighly 
magnified, from Cambridge, collected and prepared by Kev. Prof. Gwatkin, M.A. 
The Echinoglossa are not oidy remarkable for the large accessory 
oval plate or knob attached to and projecting anteriorly beyond the 
teeth, but also for the acute convergence of the transverse rows 
from the lateral margins towards the anterior portion of the membrane, 
instead of towards the posterior end as in mollusks generally. 
The individual teeth are very closely and compactly arranged, ex- 
cept near the median line, where the smaller size of the teeth leaves a 
perceptible space between the transverse rows ; the mid-tooth shows 
long and jnoniinent lateral margins, which in Phyi^a fontnialis are 
partially overwrai)iied Ijy or fused with the adjacent teeth. The 
marginals are very nnmerons and practically uniform throughout, 
varying only in the number of cutting i)oints they disi)lay. 
