ORDOVICIAN FAUNAS. 189 
subeentral, small. Surface of the shell without annulations or ridges ; 
marked by fine, crowded, horizontal lines, somewhat undulating or 
irregular, often running into one another, rounded on the summit 
and subimbricating, separated by low furrows and divided at irregular 
intervals by a furrow of more than average width. The horizontal 
lines and furrows are crossed by extremely fine, vertical lines, seen 
only under magnification.”—-Clarke. 
Remarks.—Fragments of this species of Orthoceras are sometimes 
met with in the Trenton fauna of New Jersey. One specimen, which 
is possibly a member of the species, has a length of 75 mm., with a 
diameter of 21.5 mm. at the larger and 14 mm. at the smaller end. 
This specimen does not preserve the characteristic transverse mark- 
ings of the shell, but they may have been eroded. It is marked, how- 
ever, by a series of dull-colored, vertical bands about 1 mm. in breadth, 
separated by darker bands of about twice the width. A similar band- 
ing of the shell is noted by Clarke, and is considered by him as being 
a trace of original color lines in the living shell. 
ORTHOCERAS TENUITEXTUM (Hall). 
Plate XIII., Figs. 3-4. 
1847. EHndeceras proteiforme var. tenwtextum Hall, Pal. N. Y., vol. 
I., p. 210, pl. 45, figs. 2-5. 
Description.—Shell straight, gradually expanding. Sutures, septa 
and sipho not observed. The surface is marked by a series of fine, 
angular, longitudinal, raised lines, about three or four occupying the 
space of 1 mm., and also by transverse, raised lines, more rounded 
and a little closer together than the longitudinal markings, giving to 
the entire surface a fine, regular, reticulate ornamentation. 
The dimensions of the best specimen observed are: length, 54 mm. ; 
diameter at larger end, 13 mm.; diameter at smaller end, 5.5 mm. 
This specimen is somewhat compressed, so that the diameters given 
above are a little too great. 
