Remarks on the Genera Ectomaria , Koken, and Hormotoma , Salter, with Descriptions of British Species

Abstract

I n my previous papers on the Carboniferous Murchsoniæ I have given some account of most of the different genera or sections into which the family Murchisoniidæ has been divided. It is not, therefore, necessary to refer to many of these again, as I am here only describing the British members of one of these established genera, namely Hormotoma , Sailer, and also of the new genus Ectomaria , Koken. These two genera contain some of the oldest known species of elongated gasteropoda. They are both distinguished from the typical Murchisoniæ by merely possessing a sinus in the outer lip, instead of having a deep narrow slit with parallel edges; also the lines of growth retreat towards, and advance from, the sinus more obliquely. The protoconch, which throws so important a light upon the affinities of the gasteropoda, is so far unknown in Ectomaria and Hormotoma , neither has it been found out whether these shells have opercula. In the present state of our knowledge it is doubtful in what degree these genera are related either one to another, or to the typical Murchisoniæ . Hormotoma agrees with Murchisonia therein that the sinus gives rise to a band, though it is generally somewhat indistinctly limited ; whereas Ectomaria can hardly be said to possess a band, the greatest sinuosity of the lines of growth being merely situated between two keels. Koken does not place Ectomaria in the Murchisoniidæ, and it is not clear to which family he would refer it ; apparently it stands in