146 Fossil Shells from the Colorado Desert. [ March, 
- Mr. Tryon reporting on certain shells collected by Lieut. 
Wheeler’s expedition in Utah Territory, says, 
“Included -in the collection are two specimens of the genus 
Tryonia Stimpson. This curious little genus was heretofore con- 
sidered to be restricted to the Colorado Desert of southern Cali- 
fornia. wo species have been described, viz: the type 7. 
(Melania) exigua Conrad, of which Melania protea Gould is a 
synonym, and 7ryonia clathrata Stimpson. The two Utah speci- 
mens are probably 7. exigua.” 
The lump of earth from which the specimens mentioned were 
obtained was about the size of one’s fist, yet this comparatively 
small matrix contained as many as three hundred. What an in- 
conceivable number must have been propagated and buried here, 
what numberless generations have been born and died, since the 
lowest foot in this perpendicular well-section was deposited, to 
the last and most recent deposit, when the present surface was 
reached and completed! If the mind is unable to comprehend 
what is equally imperceptible to the eye, the numbers buried ġe- 
neath the surface, the mind also fails to comprehend what és visi- 
ble to the eye, the vast number which are seen oz the surface of 
the desert in crossing it, the external skeletons of the vast multi- 
tude left on the top of the last deposit, when the last inch of water 
evaporated and left a sterile and windswept waste, upon which 
to-day are scattered untold millions of these tiny forms. 
If we may assume that the species to which these forms belong 
no longer exist, within the more special area under consideration, 
they must have become extinct within geologically a very re- 
cent time. An examination shows the sculpture to be wonder- 
fully sharp and well defined, yet probably the life of these 
minute organisms, that is to say, the specific life, had an ear- 
lier genesis than that of the human race, and the particular 
specimens before us were living, at a time, prior to the appear- 
ance of man on the planet. 
We have here also an illustration of the relation of life and 
species to environment, as shown in the extinction of the former, _ 
through a radical change in the latter. 
In connection with the total evaporation of the former lake or 
lagoons as above, it should not be inferred therefrom that the 
particular portion of the desert incidentally under consideration, 
1 Proc. Phil. Acad. Nat. Sciences, May 1, 1873. 
