506 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



other fossils, such as shells, &c., composed of calcareous matter, embedded in 

 the same matrix, retain their original substance. 



The only specimen discovered unfortunately had its shaft broken away 

 and lost at the time the mass of rock in which it was found was broken open. 

 The expanded part is about 1.60 inches in length and 0.90 inch in breadth ; 

 its greatest breadth being slightly behind the middle. Posteriorly, it is 

 obtusely angular, while its lateral alations have their margins converging 

 with convex outlines from the central region, or slightly behind it, forward. 

 The midrib is quite slender, and the striae of the alations are fine, rather 

 obscure, closely arranged, straight, parallel, and directed backward and out- 

 ward at an angle of about 70° from the midrib. 



As already mentioned, this fossil seems allied to Loligo Bollensis, Schou- 

 bler, especially in the surface-striations and general form of its expanded 

 part. It wants the lateral sinuosities of that species, however, and evidently 

 had a more slender midrib. 



Locality and position. — Moreau River, Dakota ; from the Fox Hills 

 group of the Upper Missouri Cretaceous series. 



ARTICULATA. 



ANNULATA. 



TUBICOLA. 



SERPULIDiE. 



Genus SERPULA, Linnaeus. 



Synon.—SerpuJa, Linnaeus (1758), Syst. Nat. (ed. 10), 1767.— Brug. (1792), Eucyc. Me"th., I, xiv.— Cuvier 

 (1798), Tab. fildm., 622— Lamarck (1801), Syst. An., 325.— Blainv. (1827), Diet. Sci. 

 Nat., XLVIII, 549. 



Etym. — Serpo, to creep. 



Exawp. — Serpula vcrmicularis, Linnaeus. 



Tube calcareous, procumbent, variously curved, or spirally coiled, grow- 

 ing singly or in groups, attached to marine bodies, and capable of receiving 

 the entire animal; aperture at the larger extremity simple, rounded, and 

 provided with a discoid or funnel-shaped operculum. 



This genus is nearly related to Spirorbis, which some authors include as 

 a mere section of the same group. As these two types, however, differ in 



