BRACHIOPODA. 91 



1S76. Kutorgina, Linnarsson. Bi-achiopoda of the Paradnxides Beds of Sweden, p. 25. 



1877. Kutorgina, Hall and WntTFiELD. U. S. G-eolog-ical Exploration Foj-tieth Parallel, p. 207. 



1883. Kutorgina, Davidson. British Silurian Brachiopoda, Supplement, p. 212. 



1884. Kutorgina, Walcott. Palseontology Eureka District, pp. 18-21. 



1885. Kutorgina, Matthew. Illustrations of the Fauna of the St. John Group, No. 3, p. 42. 



1886. Kutorgina, Walcott. Bulletin No. 30, U. S. Geological Survey, pp. 101-107. 



1887. Kutorgina, Walcott. American Joui-nal of Science, vol. xxxiv, p. 190. 



This genus was founded by Mr. Billings on certain obelloid fossils which he 

 had previously referred to the genus Obolella. In a foot-note to his descrip- 

 tion of the species Obolella dngulata, he suggested* the deviation of this form 

 from O. chromaiica, in the elevation of the beak of the dorsal valve, which in 

 his judgment implied an area and probably a foramen. The muscular impres- 

 sions were indicated as " two large, oval impressions faintly impressed, but still 

 distinctly visible " with " no trace of the lateral scars." The name Kutorgina 

 was proposed in the event of this species not proving congeneric with 0. chro- 

 matica. 



Among subsequent students of these fossils, no one has given so thorough a 

 discussion of their characters, or has had access to such complete material, as 

 Mr. C. D. Walcott. We therefore present the diagnosis of the genus as for- 

 mulated by him.f 



" Shell inequivalve, transverse or elongated ; hinge-line extended nearly to 

 the width of the shell. 



" Larger or ventral valve convex, elevated at the beak, which is straight or 

 incurved, with or without a mesial sinus ; area narrow, or without a true area ; 

 when present it is divided by a wide open fissure. Smaller or dorsal valve flat 

 or slightly convex, beak marginal. 



" The areas of both the ventral or dorsal valves of the species which we have 

 showing them, are very narrow, and the fissure between them broad and rela- 

 tively large. A number of thin longitudinal sections, cut so as to cross the 

 beak, and also out on the cardinal edges, fail to show any covering to the fissure, 

 and the area appears a little more than the reflexed shell, as the lines of growth 

 of the valve extend over and upon it. 



" Exterior of valves marked by concentric strise or lines of growth that 

 terminate on the cardinal edges of the valves, as in K. dngulata; nearly smooth 



* Geolog-y of Vermont, p. 948. 1861 ; Pateozoic Fossils, vol. i, p. 9. 1865. 

 t Bulletin No. 30, U. S. Geological Survey, pp. 101, 102. 



