On some of the Proterozoic Gasteropoda which have been referred to Murchisonia and Pleurotomaria, with Descriptions of New Subgenera and Species

Open Access
Publisher Website
Google Scholar
Abstract
Introduction. After the creation of the genus Murchisonia by A. d'Archiac & E.de Verneuil in 1841, most of the Palæozoic, Turritella -like, banded gasteropoda were referred to that genus by later writers. Recently attention has been drawn to the fact that these shells do not all agree with the type, and that there are at least two separate groups, each distinguished by a different form of the outer lip. The typical group is characterized by a slit of greater or less depth in the outer lip, with parallel edges, which is represented by a band on all the whorls. The other group is characterized by having merely a sinus in the outer lip, which in some cases gives rise to a band more or less distinctly limited, while in others it is not defined in any way. Some of the oldest-known gasteropoda, both elongated and short, have an opening in the outer lip; and as, owing to age and the manner of fossilization, very few have the outer lip well preserved, it is difficult to arrive at a correct conclusion as to its structure, more especially as the form of the lines of growth on the whorls rarely shows the actual depth of the sinus in the outer lip when mature. In the adult the outer lip frequently advances, thus rendering the mature sinus much deeper than the indications of it in the earlier stages of growth. The existence of a true slit in the outer lip, with a break in

This publication has 0 references indexed in Scilit: