Having recently had the opportunity of carefully investigating the genus Tentaculites, I was led to the conclusion that several fossils of diverse zoological affinities had been included under this head, and that the prevalent differences of opinion as to the systematic position of this genus might be thus readily explained (American Journ. of Science and Arts, vol. iii., no. 15, 1872). Originally founded by Schlotheim in 1820 (Petrefact. i., p. 377), Tentaculites, as its name implies, was believed to comprise fossils which were nothing more than the slender terminations of the jointed arms of Crinoids. Modern palæontologists have been divided in opinion as to whether Tentaculites was truly referable to the Tubicolar Annelides or the oceanic group of the Pteropoda— most recent authorities placing the genus in the latter class. In point of fact the difficulty has really arisen from the circumstance that two dissimilar sets of fossils have actually been included under Tentaculites; some of these being genuine Pteropods, whilst others are equally genuine Tubicolar Annelides. As all the typical species belong to the first group, it follows that the genus Tentaculites remains a Pteropodous one; whilst the Annelidan forms must be referred to new genera.