PLATE 15. 



Fig. 1. 89. 1. Ormoceras tenuifiluh. (Ptig. 66.) 



1. A fragment of this species, partially covered with the delicate thin outer shell, presenting in the lower 

 part of the figure some obscure markings of the septa ; and above, showing the moderate convexity of 

 a septum. 



1 a. Transverse section of the same specimen, broken through the annulations of the siphon. 



I b, A portion of the outer shell magnified, showing the fine undulating threadlike lines upon the surface. 



1 e. A longitudinal section of a portion of a large individual, showing the septa, which are composed of double 

 plates reaching only to the inner lamina of the exterior shell. The distance between the laminae is 

 unusually great in the upper part of this specimen, the spaces between them being nearly as great as 

 between the septa. 



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