124 THE DEVONIAN OF MISSOURI. 



Orthoceras cf. atreus Hall 

 Plate 30, figure 3 

 1879. Orthoceras Atreus Hall, Pal. New York, vol. V, pt. 2, p. 305, pi. 88, fig. 1; pi. 

 89, figs. 10 and 11. 



Hall's description — "Shell large, straight, robust, very regularly and gradually 

 enlarging to the chamber of habitation. Transverse section circular. Apical angle 

 about 6 degrees. Initial extremity unknown. 



Chamber of habitation sub-cylindrical, well developed; length about three times 

 the diameter of the tube at the last septum. Tube with a very broad and gentle con- 

 striction anterior to the middle of the outer chamber, and the indication of a contrac- 

 tion at the aperture. 



Air-chambers regular, deep, having a depth of fourteen mm. where the tube has a 

 diameter of fifty-five mm. The external walls are smooth in the cast, with a slight longi- 

 tudinal carina indicating the ventral side. 



Septa smooth, so far as observed, with a concavity equal to an arc of 120 degrees. 

 Sutures straight and horizontal. 



The siphuncle, as determined from a small fragment referred to this species with 

 some doubt, is large and excentric, having a diameter at the septa of five mm., where 

 the tube has a diameter of fifty mm., and distant from the nearest margin of the septa 

 about one-third the diameter of the tube. It is expanded in the interseptal spaces, 

 as indicated in a longitudinal section." 



Remarks — Fragments of the species are not uncommon but no good specimen has 

 been collected. The best specimen is 25 centimeters long and 12 centimeters in dia- 

 meter at the base of the living chamber. The part of the living chamber preserved is 

 10 centimeters long. The air chambers are 18 millimeters deep. By projecting the side 

 lines an angle of 12 degrees for the apex is obtained. 



Occurrence — Snyder Creek shale, Callaway County. 



Family Nautilidae 

 Genus Nautilus Linneaus 

 Nautilus? lawsii? Swallow 

 1860. Nautilus? Lawsii Swallow, Trans. St. Louis Acad. Sci., 1, p. 658. 



Swallow's description — "Shell very large; septa very numerous and very convex; 

 volutions depressed on the dorsal surface, somewhat flattened on the sides, and flat- 

 tened or concave on the inner surface; taper gradual; aperture elliptical. 



Diameter of the shell, 10.75 inches; length of aperture, 4 inches; width, 3.25." 

 Remarks — The writer has not seen a closely coiled specimen in the Missouri faunas 

 and is listing this on Swallow's authority. 



Occurrence — Probably from the Snyder Creek, Callaway County. 



Suborder Cyrtochoanites 



Family Ooceratidae 



Genus Cyrtoceras Goldfuss 



Cyrtoceras? sp. undet. 



Plate 29, figure 4 



Description — The only specimen of Cyrtoceras in our collections consists of 19 



septae and three inches of the living chamber. The 19 septae occupy a distance of about 



13 centimeters. The specimen is only a slab, less than an inch in thickness, flaked off 



from a large specimen. 



Occurrence — Snyder Creek shale of Callaway County. 



