IIAI.OI ..... A 



- rr 



The specimen described is a fragment which is worn through the center of 

 the si|duincli>. I lie proportions of this part of the fossil and the great distance of 

 the septa contract very -tron^ly with the Orm 'initilni. and with other known 



-p.-. -if- ..f tin- L'fiiii-. 



1 hi- -].e-ie- iii-cur- in tlie higher part of the Trenton limestone, near Water- 



tnwil. .lellersoll COUIltV." 



A large specimen from Cannon Falls Minnesota, measuring upward of 300 nun. 

 in length, much more complete than the original specimen of Ormoceras remotiscpium, 

 has the dimensional characters of the latter, and upon sectioning a few of the air 

 chambers it shows a sipho in all respects like that of the type. The shell has been 

 somewhat compre->ed. giving it a subelliptical cross-section where it was normally 

 circular. 



The rate of expansion of the conch is very slow as shown by the fact that at 

 the lower end the diameter is 46 mm., while at the upper end, the length of the 

 specimen being 350 mm., the diameter is 70 mm. The portion preserved retain- 

 no part of the body-chamber, and in this length of 350 mm. there are thirteen 

 an -chain! ers, which increase considerably in depth from below upward, the lir.-t 

 having a depth of 20 mm., the last of 33 mm. The sutures are normal and regular, 

 possibly a little inclined towards the siphonal side, while the septa are deep and 

 regularly convex. The sipho is large and submarginal. At the 7th septum, counting 

 from below, the tranverse diameter of the sipho is 20 mm., that of the septum 58 

 mm. In section it proves to be decidedly constricted at the septa and makes a 

 broadly nummuliform expansion in the air-chambers, its diameter there being one- 

 third greater than at the septa. It is very thick-walled and is penetrated vertically 

 through the center by a narrow canal or endosiphon which gives off more or less 

 irregular branches into the substance of the endosiphonal wall. In the relative depth 

 of the air-chambers and the general form of the shell this species presents an 

 external resemblance to Hall's Orthoceras amplicameratum, from the Trenton lime- 

 stone at Middleville, N. Y. In that species, however, the sipho appears to be small 

 and suggests no relationship to Adinoceras. 



Formation and locality. The single specimen observed Is from the Trenton llmeatone at Cann M, 

 Falls, Minnesota. Collection of W. H. Scodeld. 



Family ORTHOCERATID^E 

 Genus ORTHO I I, \s. Hreyn.. 1732. 



The material representing this genus is measurably abundant, but not in very 

 favorable condition for identification, and probably represents a greater number of 



