Excerpt from Notes on the Pleurotomidae With Description of Some New Genera and SpeciesThese tribes are not all rigorously isolated or strongly de limited and there are several generic types before me which, from general appearance, may prove to be annectant or doubtfully referable to any of them, but they serve very well in a broad way and there is very seldom any doubt as to the proper reference of a species by its general facies alone. The genus Tomella may perhaps best serve as an illustration of these aberrant forms. This genus, while evidently bearing a phylogenetic relationship with Perrona, as shown by the embryo and nepionic whorls, differs so greatly in other charac ters that it not only cannot be regarded as at present closely allied to Perrona, but must be considered one of the most remarkable genera of the entire family. While evidently a member of the tribe Pleurotomini, it departs from its most significant characteristic in possessing a large deposit of callus at the posterior limit of the aperture, though, upon closer observation, it can be perceived that this callus in not quite homologous with the posterior tumid callus of the Clavini and is probably formed in a different way. The chief peculiarity of Tomella resides in the form and anterior position of the anal sinus, and in the fact that this sinus is wholly covered and concealed from view by the successive growth of the shell, so that. It does not appear upon the spire whorls - a character which isolates it completely in the family.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.