II.M.or. Ml] 



Uocon-ru rrvcrl.) 



This specie* i- 'li-tmLrui-ii.'.l i,\ it- -ukicute venter, broad hut not ventrirose 

 surface ami tlic very slight decrease in the diameter of the body-chamber 



from it- ki-> to the con-friction. 



Kifioii ami U-ality.The specie* appears to )H< unite (illinium ill UK- lower liinr In-ils nf tin- 

 Trriiton linn-toil.- ut Janesvllle, Wisconsin. It also iKvut-- In th<> Tn-iit-m at PrenU>n and Minneapolis. 



MiMii.--i>ta. 



Mtuntm RfffiMter, No. 8300. 



OKOOO*BAB OARVKRI. -/' ' 



. K I.V1II. KliiS. 7-. 



An entire hody-chamber, with three air-chambers attached, is characterized by 

 it- l>roa>i -i'lc-. narrow dorsum and compressed, subangular venter. The cross- 

 section of the shell is, thus, elongate-ovate, its major and minor diameters being as 

 3 to 2. Above the third septum (counting from the aperture) the shell expands 

 somewhat to within the base of the body-chamber and is, thence, gently contracted 

 to the aperture. The latter is more narrowly ovate than the rest of the shell, its 

 lateral margins convex, making a narrow eraargination on the venter. The suture 

 i- transverse on the sides and dorsum, without curvature, but is curved forward 

 over the venter to such a degree that the depth of the air-chambers at the ventral 

 -urface is about twice that on the dorsal surface. 



The sipho is ventral and is situated within the margin of the septa. 



The shell is bnt slightly arcuate, being suberect except in the vicinity of the 

 aperture where it is curved inward making the aperture somewhat oblique. Sur- 

 face covered with fine concentric striae which are strongly recurved over the 

 venter, concentric to the outline of the aperture. The length of the body-chamber 

 in the specimen is 20 mm.; the entire length of the body-chamber with three air- 

 chambers, 26 mm.; the major diameter of the third septum, 21 nun .. the minor 

 diameter, 14 mm. 



formation and locality. lt> ih<' Tr.-ntoo limestone at Minneapolis, Minnesota. A fragment of a 

 larger obeli hao also been observed In the upper buff beds at Rockton, Illinois. 



Mtueum RegitUr. N 



ONOOCERAS DOUOLASSI, sp. 



PLATE LXI. FIOB. tt-15. 



Shell arcuate over the earlier portion, suberect for the greater part of its 

 length. From the eighth air-chamber (counting from the aperture) upward, the 

 shell expands rapidly to the last septum, thence contracts more rapidly, forming a 

 broad and rather deep constriction just within the aperture. The expansion i- 



