Notes on the Genus Murchisonia and its Allies; with a Revision of the British Carboniferous Species, and Descriptions of some New Forms

Abstract

I. T he S ubdivision of the G enus M urchisonia and its A llies 17 a previous paper 1 I gave an account of the establishment of the genus Murchisonia by D'Archiac and De Yerneuil, and described its characteristics. Since that date several new subdivisions of the genus have been made by pal~eontologists, and however reluctant we may be to introduce new terms, we cannot well avoid doing so, for many of the Murchisoniæ vary considerably from the type. Palmontologists differ both in the divisions that they adopt and also in the value that they attach to them. While some merely consider these as sections, others regard them as subgenera, or even distinct genera. Before proceeding to examine these divisions it may be well to enumerate the generic characters of Murchisonia as now defined :— Shell elongated, turreted, composed of more than six gradually increasing whorls. Whorls more or less angular, variously ornamented or smooth. Mouth oblong, oblique, terminated at the base by a very short or truncated canal. Columella arched. In the outer lip there is a narrow and more or less deep slit with parallel edges, the successive filling-up of which during the growth of the shell produces a continuous band throughout the whole length of the spire. This band is distinctly defined, and composed of either a single or double keel. Umbilicus open or closed. Though D'Archiae and De u do not indicate any particular species as type, the first mentioned on the list that they give has generally been accepted