On the Cladophora (Hopk.) or Dendroid Graptolites collected by Professor Keeping in the Llandovery Rocks of Mid Wales

Abstract

The forms of Cladophora collected by Professor Keeping from the Llandovery rocks of Cardiganshire are, regarded collectively, of a type almost new to British palæontology. Although intimately allied to the well-known dendroid species of the Quebec and Arenig formation, they are very distinct in their minor features. They are essentially of a Silurian (Upper) facies, and they remind us strongly of a group recently made known to us through the researches of Mr. Spencer, of Toronto, which characterizes the Clinton and Niagara Groups of New York and Upper Canada. None of our examples shows the complete polypary, or affords distinct proof of the presence of all the more minute classificatory features; but there is satisfactory evidence of the presence of at least four distinct genera and seven species. The genera represented are Dictyonema , Hall, Calyptograptus , Spencer, Acanthograptus , Spencer, and Odontocaulis , Lapw. Dictyonema is a well-known British genus; the remainder are new to British palæontology. Calyptograptus and Acanthograptus have been already briefly noticed from American strata by Mr. Spencer, but have not hitherto been figured. Odontocaulis is a new genus, of a peculiar type. Of the seven distinct species recognizable, four (viz. Dictyonema z.orrugatellum, Caly_ptograptus plumosus, C. digitatus , and Odontocazdis Kee_pingii ) are as yet peculiar to the Mid-Wales area. The remaining three have already been recognized by myself in the Silurian rocks of the south of Scotland. Dictyonema venustum certairdy occurs in the Upper Gala group of Selkirkshire (Llandovery-Tarannon), and doubtfully in strata of a little older date in the Girvan