NATURAL SCIENCES OF PHILADELPHIA. 205 
Centrals with a base of attachment longer than wide, the lower 
lateral angles but little expanded, the lower margin incurved, the 
upper margin squarely reflected ; reflection large, wide, with small, 
in some species almost obsolete, side cusps, always bearing distinct, 
well developed cutting points; and a very stout median cusp, 
bearing a stout cutting point which usually projects beyond the 
lower edge of the base of attachment. lLaterals like the centrals, 
but unsymmetrical by the suppression of the inner lateral angle 
of the lower edge of the base of attachment and the inner side 
cusp and cutting point. The transition from laterals to marginals 
is shown in pl. IX., fig. 8 (4. spinosa). It is, as usual, produced 
by the comparative lesser development of the inner cusp and 
greater development of its cutting point. This cutting point 
becomes bifid, the reflection becomes shorter, the cutting points 
more produced, and thus gradually the form of the marginal teeth 
is reached. They are low, wide, the reflection equalling the base 
of attachment, the cutting points long, oblique, usually two in 
number, the inner one generally, and the outer one rarely, bluntly 
bifid: the outer bifurcation of each is more produced than the 
inner. There is great variation in the denticulation of the mar- 
ginal teeth even on the same lingual membrane. A transition from 
laterals to marginals similar to that of H. spinosa is found in ZH. 
barbigera, Edvardsi, stenotrema, hirsuta, germana, and monodon. 
There seems no difference in the characters of the teeth of the 
different species examined: by me, excepting the slight one of the 
greater or lesser development of the side cusps of centrals and 
laterals, especially the former; whether this is constant can only 
be proved by a careful examination of every portion of each lin- 
gual. In H. hirsuta I found these cusps more developed than in 
the other species (pl. IX., fig. 6). 
The count of the teeth in the different species is as follows :— 
H. spinosa (pl. IX., fig. 8) has 27—1—27 teeth; 9 perfect 
laterals. 
H. Edvardsi (pl. 1X., fig. 1) has 20—1—20 teeth; 9 perfect 
laterals. | : 
H. barbigera (pl. IX., fig. 9) has 21—1—21 teeth; 8 perfect 
laterals; but even the third has its inner cutting point greatly 
produced. : 
H. stenotrema (pl. IX., fig. 7) has 20—1—20 teeth; 10 perfect 
laterals. 
