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The figure by Holm, p. 763, shows conclusively that the sutures 

 in the nepionic stage are straight, Trocholites like, and quite dis- 

 tinct from those of the later stages. The narrow annuli cross the 

 whorl during the ephebic stage or first part of the free whorl, with 

 the true Ancistroceran curves, namely, with shallow ventral sinus 

 between two low, narrow ventro-lateral crests, broad, shallow lat- 

 eral sinuses and a very slight but perceptible dorsal sinus not 

 divided by a crest, as in Lituites. 



These change in the gerontic stage, the ventral and dorsal sin- 

 uses being replaced by low, broad crests, the lateral sinuses alone 

 remaining. This stage repeats exactly the degenerate characters of 

 the curves in the lines of growth of the ephebic stage of Rhyncortho- 

 ceras and show, together with other facts, that we are dealing with 

 a degenerating series. The siphuncle is dorsad of the centre in 

 the ephebic stage, but it is nearer the centre than in Lituites. 



This genus does not seem to stand in the line of modifications 

 leading from Lituites to Ancistroceras, nor in that leading from 

 Lituites to Rhyncorthoceras. 



Ophidioceratidce . 



The apertures and costated whorls of Ophidioceras have been 

 supposed by several authors to show that it belonged in the family of 

 the Lituitidae. The apertures are, however, distinct, having only 

 three large sinuses and a corresponding number of crests and the 

 costations and lines of growth have not the peculiar forward bend- 

 ing lateral curves of the Lituitidae. The ornamentation of the 

 younger stages and the form of the nepionic stage is so widely dif- 

 ferent that no close comparisons can be made with the young of 

 Cyclolituites, the closest coiled form of the Lituitidae. 



This genus was formerly supposed by the author to belong in the 

 same group with Ascocerasand Glossoceras, which had similar aper- 

 tures, but recent investigations have shown that these genera are 

 widely separated in structure. 



Ophidioceras. 



This genus, fully described by Barrande, becomes very interest- 

 ing in the history of the impressed zone on account of its highly 

 ornamented and costated whorls and the peculiar, excentric charac- 

 ter of the free, whorl and the aperture with deep, narrow hypono- 



