Some British Trilobites of the Family Calymenidæ

Abstract

I. Introduction The study of the Calymenidæ was begun with the re-examination of the figured specimens and described types of the British species, and the results of this work have already been published (Shirley, 1931, 1933). An extensive series of British and foreign specimens has been examined. It is believed that the results obtained are of general application to the whole group of the Calymenidæ or at least provide a basis for further research. Perhaps not the least interesting of these results is the discovery that certain species had wide geographical range but apparently a comparatively short existence. Such species are valuable for purposes of correlation over extensive areas. The mode of preservation of the trilobite test has a marked effect upon the ease of identification of specimens. The complete preservation of the dorsal test is relatively infrequent in the geological sequence of the British Isles. The greater proportion of the material is in the form of separated pieces representing the scattered portions of the cast tests or the broken remains of the test after death. This scattering of the parts often makes identification difficult. II. Preservation of Material In limestones and some calcareous deposits, such as the Silurian limestones of Dudley, Worcestershire, and the Ordovician calcareous grits of Hoar Edge, Shropshire, the test is preserved almost in its original condition. In some specimens the ornament is preserved in every detail, though too often it has been destroyed by the acid used to clean away the matrix. The best method