NATURAL SCIENCES OF PHILADELPHIA. 217 
is, however, one Mexican species, one African, and one Huropean, 
H. arbustorum. The jaw of the last agrees with our species. 
The lingual membrane is long and narrow. Fig. 60 shows the 
general arrangement of the teeth upon the lingual membrane. 
The characters of the individual teeth are shown in my plates. 
I have selected H. Stearnsiana pl. XIIL., fig. 3, to give an idea of 
the teeth in successive transverse rows. Fig. @ shows a group of 
central and lateral teeth in two adjacent rows, } the transition 
from laterals to marginals, c marginal teeth from near the outer 
edge of the membrane. The central teeth have a base of attach- 
ment much longer than wide, with incurved lower margin and 
expanded lower lateral angles ; the upper margin broadly reflected ; 
reflection short, stout, with subobsolete side cusps bearing no cut- 
ting points, and a stout, long median cusp bearing a short, blunt 
cutting point, which does not reach the lower margin of the base 
of attachment ; the reflection with the median cusp is pear-shaped ; 
in many species there is a duplicate line of reenforcement parallel 
to the upper margin of the base of attachment. The lateral teeth 
are of similar type to the centrals, but are unsymmetrical by the 
suppression of the inner, lower, lateral angle of the base of attach- 
ment. The outer laterals have a side cusp and cutting point. 
The transition from laterals to marginals is formed by the greater 
proportional development of the cutting point, the lesser develop- 
ment of the cusp; the cutting point then becomes bifid, the re- 
flection becomes more nearly the same size as the base of attach- 
ment, and thus the true marginals are gradually reached. These 
last are longer than wide, have a base of attachment smaller 
than the reflection and cut away on its lower inner angle; the 
reflection is produced into one long, sharp, oblique, bifid cutting 
point, the inner division the smaller, and one outer, much shorter, 
sharp, rarely bifid cutting point. 
Most of the species examined agree in dentition with Stearnsi- 
ana. Some have more blunt cutting points to their marginals, as 
H. sequoicole (pl. XIV .,fig.5), but even on various parts of the same 
membrane the marginals vary in this respect. In Kelletti, Stearn- 
siana, tudiculata, arrosa, Traski, sequoicola, Ayresiana, redimita, 
Vicklinvana, ramentosa, exarata, I have failed to detect any side 
cutting points to the central and inner lateral teeth. I found the 
points, however, in H. rujicincta (pl. XIV., fig. 3). H. Town- 
sendiana (pl. XVIII., fig. 8) has these cutting points and side 
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