YAKUTAT FOSSILS 
I 4 I 
poned to some future occasion when we hope to discuss the 4 fucoids * 
as a whole. For the present it will suffice to state that the spiral habit 
of growth is the character principally relied on in distinguishing the 
genus from the other unbranched fucoids. The much more robust 
Cylindrites convolutus Fischer-Ooster, from the Eocene of the Alps, 
also grows in a spiral manner, but in this case the spiral is formed by 
a single cord and not by two parallel cords. 
The name is from that of the discoverer, Mr. G. K. Gilbert, who 
also collected most of the other fossils obtained by the geologists of 
the Expedition from Pogibshi Island. 
Gilbertina spiralis sp. nov. 
pi. XVIII, figs. 1,2. 
The spirally coiled slender stem begins with an open loop, the two 
ends of which soon begin to curve inward and, maintaining a nearly 
parallel curve with respect to each other and preceding volutions, con¬ 
tinue until they cover a subcircular space 5 to 8 cm. in diameter. The 
concave spaces between the coils of the stem increase in width as 
growth proceeds, from about 1.2 mm. to about 2.5 mm., while the 
thickness of the stem itself remains nearly constant at about 1.0 mm. 
Perhaps it would be nearer the truth to consider the raised coils of 
the fossil as matrix filling the interstices between an originally hollow 
and now compressed cylinder. Under this interpretation the structure 
at the center of the coil would necessitate the assumption that the im¬ 
pressions were formed by two equal but separate cylinders. This was 
the view that first suggested itself, but the difficulty of explaining the 
irregularity of the outer one or two of the raised coils exhibited by 
two of the specimens before us could not be satisfied except by the 
interpretation adopted above. 
Locality .—-Pogibshi Island, opposite the village of Kadiak, Alaska. 
Collector* — G. K. Gilbert. 
Genus Helminthoida Schafhautl. 
Helminthoida Schafhautl., Geognostische Untersuch. des siidbayer. Al- 
pengebirges, p. 142, 1851. — Heer, Urwelt der Schweiz, p. 246, 1865, 
and Flora Foss. Helvetia, p. 167, 1877. 
Among the problematical fossils before us are four varieties of a type 
that in part at least corresponds very closely with the one for which 
Fleer proposed the name Helminthoida. The first and the second of 
these varieties may be referred to this genus without reserve, but the 
third and fourth varieties depart from the normal forms of the genus 
