518 
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. 
Ophidioceratide. 
The apertures and costated whorls of Ophidioceras have been 
supposed by several authors to show that it belonged in the family of 
the Lituitide. 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 Lituitide. 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 Lituitidee. 
This genus was formerly supposed by the author to belong in the 
same group with Ascoceras and 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- 
PROC. AMER. PHILOS. SOC. XXXII. 143.3 M, PRINTED JULY 10, 1894 
