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Species of the Genus Dimorphoceras in the Bowland Shales

Published online by Cambridge University Press:  01 May 2009

E. W. J. Moore
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Extract

The genus Dimorphoceras was instituted by Hyatt, the genotype being Goniatites gilbertsoni (Phillips). The shells are involute and compressed, having the umbilicus very small or closed. The test shows fine lines of growth and a deep hyponomic sinus. Dimorphoceras is differentiated from other goniatites by having either one or both of the sutural lobes sub-divided by a small subsidiary saddle. Specimens are not generally abundant; and owing to the feeble ornamentation of the test, distinction between species is impossible unless uncrushed specimens showing sutures are obtained.

Type
Original Articles
Information
Geological Magazine , Volume 67 , Issue 4 , April 1930 , pp. 162 - 168
Copyright
Copyright © Cambridge University Press 1930

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References

1 Since the foregoing was written I have found a young specimen of N. hawkinsi. Diam. = 11·4 mm.; thickness = 4·6 mm. Umbilicus closed. The test, as seen in small portions preserved, is thin and marked with fine spirals, about six to the mm. over the venter, and slightly further apart over the sides. The external saddles have parallel sides, and curved pointed ends as in an arch. This feature agrees with that in the specimen from Gill Beck, where the external saddles in the younger part have less divergent sides than those in the older part of the shell. This specimen was found in the G. subcircularis band, Dinckley Ferry. (See U.S. Geol. Surv. Bull., 544, pl. xxxv.)Google Scholar