DEVONIAN FAUNAS. 275 
convex, in the variety arata much more so, and they are apt to have a 
proportionately greater width. The surface markings are also 
different, although in both forms they consist of alternating larger 
and smaller ridges or striez. In the Coeymans limestone specimens 
there is a greater difference between the coarse and fine markings, the 
coarser ridges being less sharply angular, with about five or six ex- 
ceedingly fine filiform striz in the intervening spaces. In the Manlius 
limestone specimens the median portion of the pedicle valve is usually 
rather broadly flattened toward the front, while in the Coeyman’s lime-_ 
stone individuals no such flattening is observable. The average forms 
in the two faunas certainly exhibit sufficient differences to be ranked 
as distinct species, although they are doubtless genetically related, 
and are probably connected by intermediate forms. The material in 
the New Jersey collections is not sufficiently well preserved nor suffi- 
ciently abundant to permit the proper limitations and relationships 
of these forms to be shown, but with the proper material for study it is 
quite probable that it would be found necessary to recognize two dis- 
tinct species now included in Strophedonta varistriata. 
STROPHEODONTA VARISTRIATA var. ARATA H. 
Plate XXVIIL.; Wig. 3. 
1859. Strophodonta varistriata var. arata Hall, Pal. N. Y., vol. III., 
p. 183, pl. 18, figs. 1 at. 
Description.—The shell referable to this variety is closely related 
to, and grades into, the typical Coeymans limestone form of S. vari- 
striata. It is a more convex and porportionately wider shell, with the 
coarser, radiating ridges more angular and stronger, with a smaller 
number of intervening, finer striae, which are really placed upon the 
sloping sides of the larger ridges, instead of upon a flattened area 
between adjacent ones. 
