On Lingulasrna, Etc. — Ulrich. 377 
about four thousand years it is easy to calculate the date 
when it should be at a sea-level. But the process becomes 
less and less rapid as the land becormes low and the data 
necessary for the solution of the problem are not yet within 
our reach. All these geological changes are inconceivably 
slow. Generations have come and gone and generations more 
will come and go ere any difference in our geography will be 
observable. The life of man as an individual is but a speck 
beside the aeons through which nature acts and the existence 
of man as a species scarcely more than an infinitesimal quan- 
tity beside the eras through which we have been tracing the 
existence of the great Mississippi-Missouri water-system. 
Long before these rivers have accomplished what has been 
aptly called "their contract of filling the gulf of Mexico " all 
our existing state of things will have passed away ; the face of 
the earth will become unrecognizable to those who now dwell 
on it, and possibly man, " the lord of creation " as he proudly 
styles himself, will be numbered among the extinct species of 
the globe ; his remains may be treasured in the strata of the 
future as samples of a creature that once lived, when he him- 
self has given place to some higher or possibly to some lower 
but fitter survivor in the struggle for existence. 
In the above brief sketch of a very long story many of the less im- 
portant points have been entirely omitted to secure greater clearness 
and avoid undue length. An earlier palaeozoic river on a small scale 
may have existed among the Archaean highlands of Minnesota and Wis- 
consin, and great changes of level probably occurred during the Ter- 
tiary era in the southern states. But these and many other details 
would not affect the main story. [E. AV. C] 
ON LINGULASMA, A NEW GENUS, AND EIGHT NEW 
SPECIES OF LINGULA AND TREMATIS. 
By E. O. Ulrich. 
L-INGUIiA PROCTERI, n. sp. 
Figs, la, lb, Ic. 
Shell acutely elongate-ovate, the width and length respect- 
ively as three is to five ; widest in front, narrowing gradually 
to the beaks. Front margin generally a little straightened, 
but sometimes the whole anterior third is rounded uniformly. 
Sides gently convex, converging posteriorly from the point 
of greatest width which is about two-thirds of the length from 
the beaks. Apex of the dorsal valve narrowly rounded, that 
of the ventral acute and projecting considerably beyond the 
