PLATE 2 2. 



Page. 

 Fig. 1. Heteroceras! Cheyknnense , 483 



l,fl. A septate fragment (type-speeiuieu). 



1, b. The siphonal lobe of the same, magnified ouo and three-quarter diameters. 



1, c. The antisiphonal lobe, magnified in the same way. 



Fig. 2. Heteroceras * cochleatum 478 



2, a. A fragment of the septate part of the shell, peripheral view, (type-specimen.) 



2, b. An opposite view of the same. 



Fig. 3. Hei.icoceras Mortoni, var. tenuicostatum 487 



3,0. A peripheral view of a septate fragment. 



3, b. Another view of the same. 



3, c. A septum of the same, magnified two and a half to three diameters. 



Fig. 4. Heteroceras tortum 481 



4,(i. A peripheral view of a partly septate fragment (type-specimen). 



4, b. An opposite view of the same. 

 4,c. A septum of the same, magnified. 



Fig. 5. Heteroceras? umbilicatum i-^ 



An under-side view of the type-specimen, consisting of nearly one entire, partly septate, 

 volution. 



