168 CALIFORNIA ACADEMY OF SCIENCES [Proc. 47TH Ser. 
Crepidula princeps Conrad persists from lower Miocene into 
Quaternary, and Pisania fortis Carpenter persists from upper 
Miocene into Quaternary before becoming extinct. 
Throughout the Miocene, into the Pliocene, and up to the 
present, little evolution of forms is seen. Species appear with 
all their characteristics distinctly marked, run their course, and 
disappear from our ken, without any appreciable change. The 
geologist, looking over collections from the lowest Miocene to 
the Recent fauna, rarely sees the evolution of marine inverte- 
brates. He sees only the sudden appearance of forms, and 
equally sudden disappearance of the same, without knowing 
whence they came, or how they disappeared. 
This could be used as an argument for saltatory or spas- 
modic evolution. But it could be used equally well as an argu- 
ment for special creation. In fact, the paleontologist does not 
see here any spasmodic evolution; he sees only sudden appear- 
ance. The species appear before us in the rocks, without any 
previous record or credentials as to their history—presumably 
as immigrants, having been evolved somewhere else. They 
live on a while, and disappear a few at a time. 
In the few cases where there is even a suggestion of evolu- 
tion of species, this is not spasmodic, but slow and regular. In 
the Venus shells there is a probable genetic series, from Chione 
temblorensis in the lower Miocene, through Chione securis in 
the middle and upper part of the Miocene, to the group of 
Chione succincta of the Pliocene, Quaternary, and Recent 
faunas. 
An equally good genetic series is seen in the development of 
Pecten andersont of the lower Miocene into Pecten discus and 
Pecten pabloensis of the upper Miocene. 
Another probable genetic series is that of the group of 
“Janira’; namely, Pecten sanctaecruzensis of the lower Mio- 
cene, Pecten bellus of the Pliocene, and Pecten excavatus of the 
Quaternary and Recent faunas. In this case there was a grad- 
ual retreat southward as the climate grew cooler, and the 
modern representatives are almost entirely confined to warmer 
waters. In addition to these, nearly fifty other species in the 
Recent fauna can be traced somewhat doubtfully into Miocene 
ancestors. : 
