700 
PALEONTOLOGY: W. H. DALL 
« Richards and Wadsworth, J. Amer. Chem. Soc, 38, 1659 (1916). 
7 Baxter and Grover, /. Amer. Chem. Soc, 37, 1027 (1915). 
8 Honigschmid and St. Horovitz, Sitz. k. Akad. Wiss., Wien, 123, Ila, 1 (2407) (Dec, 1914). 
He gives the name 'Uranblei' to this form of lead. The name is appropriate if, as seems 
probable, the substance may ultimately be traced back genetically to uranium, according 
to Boltwood's brilliant and well-supported hypothesis. Because the relation of this form 
of lead to radium is somewhat less remote than that to uranium, we used the term 'radio- 
lead' for it in a previous paper; but this term has also been applied to Radium D and is, 
therefore, not distinctive. The time for a final nomenclature of these substances has prob- 
ably not yet come, but the expression "isotopic lead," based upon Soddy's word 'isotope,' 
is certainly safe as applied to every substance fitting into this place in the Periodic System. 
We venture to suggest that the present permanent isotope of lead be called 'isolead,' because 
it is now by far the best known of these isotopes. If any other permanent leads are veri- 
fied, they might be called 'meta' and 'para.' For the highly transitory isotopes these 
names would be inappropriate, since they do not resemble lead in one of its most character- 
istic properties, namely, permanence. These might be called 'pseudo-leads,' giving them 
Greek ordinal prefixes to distinguish between them. But we offer these suggestions without 
any desire to be insistent, and have not even adopted this nomenclature in the present 
paper. It may well be best to retain the present nomenclature, especially as regards the 
transitory isotopes. 
' See Richards and Wadsworth, these Proceedings, 2, 505 (1916). 
ON SOME ANOMALIES IN GEOGRAPHIC DISTRIBUTION OF 
PACIFIC COAST MOLLUSCA 
By William Healey Dall 
SMITHSONIAN INSTITUTION, WASHINGTON, D. C. 
Received by the Academy, November 9, 1916 
The islands, usually called the Santa Barbara Islands, lie off the 
coast of southern California from 15 to 50 miles roughly parallel to the 
shore of the mainland, from which they are separated by a depth of 
about 400 fathoms. They range in latitude from 33° to 34°N. That 
they were formerly connected with the mainland seems probable from 
general considerations, as well as the fact that the fossil tooth of an 
elephant is reported to have been found on Santa Catalina. 
As we go south we find other islands or banks farther off shore and 
separated from the mainland by an increasing depth averaging more 
than 1500 fathoms. The Cortez Bank Hes about 120 geographical 
miles south of Santa Cruz Island of the Santa Barbara group, in latitude 
32° 20'N. It is 80 miles west of the mainland and separated by a depth 
of 1090 fathoms. 
Next comes Guadelupe Island in latitude 29° N., 200 miles south of 
the Santa Barbara islands and 150 westward from the nearest Lower 
CaUfornia mainland, from which it is separated by a depth of 1500 
fathoms. 
