Foerste.] 
296 
May 1, 
pearing much broader as seen from above. The anterior margin of 
the shell is semi-circular. The cardinal extremities are but moder- 
ately extended. 
The length varies from .62 to .79 of the breadth, usually nearer 
.62. The surface is rarely marked by strong radiating striae of 
considerable elevation as in the Clinton group specimens, bnt 
usually these striae are of more frequent occurrence on the shell, 
and the intercalated striae are still strong enough to be a promi- 
nent feature. 
3. Leptcena tenera , Shaler, from Anticosti, I have not seen, but 
judging from the description, it represents some form intermediate 
between the more common New York specimens and variety ele- 
gantula. 
4. Typical forms of Leptcena transversalis are found not infre- 
quently in New York. The ventral valve is very convex, the length 
being about .75 of the breadth. The beak is strongly incurved and 
broad. The intercalated striae are more prominent than in the less 
convex associated forms and are also often less numerous. Forms 
very similar to the typical L. transversalis of Europe are found. 
5. Leptcena area , Shaler, from Anticosti, is a small form also be- 
longing to the type of L. transversalis rather than L. sericea. Av- 
erage sized specimens are 5.7 mm. long and 8.3 mm. broad, if 
the postero-lateral angles are moderately developed ; and 9.1 mm. 
broad if these angles are more prominently developed. The shell 
is quite strongly arched anteriorly, about as much as is usual in 
ordinary New York specimens of L. transversalis. The surface 
appears quite smooth, excepting in one specimen where ten radiat- 
ing striae are readily seen with the unassisted eye. With the lens 
the customary finer striae may be distinguished. Internally, a num- 
ber of longitudinal thickenings may be seen on the dorsal valve. 
The form next to be described is similar but much more strongly 
arched. 
5. At Collinsville, Ala., in the Clinton group, are found numer- 
ous specimens of a very convex form of small size, the largest be- 
ing 7.6 mm. long and 11 mm. broad. The more frequent forms are 
7 mm. long and 8.6 mm. broad. The form is therefore seen to be 
laterally much contracted. The dorsal valve is of medium con- 
cavity with the surface rather flattened near the beak. The cardi- 
nal extremities of both valves slightly exceed the general width of 
the shell. The surface is marked by fine radiating striae, every 
