NATURAL SCIENCES OF PHILADELPHIA. 207 
characters, comparing the dentition of the other species with it. 
The centrals are longer than wide; the base of attachment has its 
outer, lower, lateral expansion but little developed, its lower mar- 
gin incurved, its upper margin squarely reflected ; the reflection is 
stout, with snibobsblete side cusps, but well- lovoloped side cut- 
ting points, and a stout, short median cusp, bearing a cutting 
point which does not reach the lower margin of the base of at- 
tachment. The laterals are like the centrals, but, as usual in the 
genus Helix, unsymmetrical by the suppression of the inner, 
lower, lateral expansion of the base of attachment and the inner 
side cusp with its cutting point. The transition teeth are charac- 
terized by the gradual lesser proportional development of the 
reflection, and greater development of the inner cutting point; as 
the teeth pass outward, this point becomes bifid, the reflection be- 
comes gradually shorter, until the true marginals are reached. 
These last are low, wide, the reflection equalling the base of 
attachment, the inner cutting point being greatly developed, long, 
oblique, bluntly bifid, the inner bifurcation the shorter of the two; 
the outer cusp is very short, blunt, sometimes also bifid. In fig. 7, 
the 10th is the first lateral showing decided modification; the 
14th tooth has its inner point bifid; the 17th tooth is a decided 
marginal. The transition from laterals to marginals is so gradual 
that it is often difficult to give the number of perfect laterals. In 
many cases, therefore, the number given by me must be consid- 
ered as only approximately correct. There is great variation in 
the denticulation of the marginal teeth. 
The general character of the dentition of the other species is 
about the same as in appressa. I found great difficulty in de- 
tecting the side cutting points in several species, especially tr- 
_ dentata and palliata. In some species I did not find the transition 
teeth or inner marginals with bifid cutting point (pl. X., fig. 3, 4). 
I give below the count of the teeth in the several species. 
i. palliata (pl. X., fig. 2) has 34—1—34 teeth; 12 perfect late- 
rals; another specimen had 14 laterals. Morse counted 115 rows ° 
of teeth. The inner cutting point of the transition teeth in this 
species is very large, as shown in c. 
Hi, obstricta (pl. X VIII., fig. 10) has 33—1—33 teeth; 10 perfect 
laterals: very like H. palliata. My figures are drawn froin that part 
of the lingual membrane which has the cutting points of its teeth 
