VI.—Notes on Jurassic Ammonites

Abstract

Two valuable pamphlets on Jurassic Ammonites have lately appeared. One of these is entitled “Cephalopodes nouveaux ou peu connus des Étages jurassiques de Normandie, par Louis Brasil.” This author, who has paid very considerable and successful attention to the Jurassic rocks in the neighbourhood of Caen, describes and figures (there are four plates) nineteen new species of Ammonites belonging to fourteen genera, viz.: Lytoceras, Phylloceras, Catulloceras, Zurcheria, Dorsetensia, Bajocia, Pæcilomorphus, Hammatoceras, Erycites, Oppelia, Cadomoceras, Strigoceras, Cosmoceras, Œcotyphius. Of these genera one is new, namely, Bajocia, founded on an unique specimen; and it must be confessed that the example is sufficiently distinct in every way to warrant this treatment. Although the author does not say so, it is evident the genus belongs to the subfamily Sonniniæ and M. Brasil practically admits as much when he states that it is very near to Dorsetensia. He further says that he considers it to be a branch from Haplopleuroceras, whose representatives have lost not only the two rows of spines, but even the keel and the furrows. We find ourselves unable to agree with this opinion, because the periphery is rounded and flattened; in our experience the keel and furrows do not disappear without leaving some trace of their former existence on the configuration of the periphery. We agree with the author that Bajocia is near to Dorsetensia, and we are inclined to think it is a late-surviving example of the stock whence Dorsetensia originated, and a “cousin” of Zurcheria.