YAKUTAT FOSSILS 14! 



poned to some future occasion when we hope to discuss the ' 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 unb ranched 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. 



Pl. XVIII, figs. I, 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 i .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. 



Helmintkoida 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 

 Heer 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 



