Transcriber Note -- Text emphasis denoted by _Italics_. OBSERVATIONS ON THE TERATASPIS GRANDIS, Hall, THE LARGEST KNOWN TRILOBITE. BY J. M. CLARKE. OBSERVATIONS ON THE TERATASPIS GRANDIS, Hall, The Largest Known Trilobite. By J. M. CLARKE. Communicated to the State Geologist December, 1890. Trilobites of great size have been reported from various formations. With rare exceptions, however, these relics are but fragments of the test, leaving to the imagination the restoration of the original proportions of the animal, and without an earnest mental effort one is apt to leave the contemplation of the large fragment with no adequate conception of the imposing lineaments of its owner. Indications of these gigantic forms occur in all the grand faunas of the Palæozoic, with the exception of the Carboniferous where diminution in numbers was accompanied by diminution in size, or, in other words, by the prevalence of genera in which great size was never attained. Almost with the earliest known appearance of the Trilobites the genus PARADOXIDES attained magnificent proportions. _Paradoxides Harlani_, the well-known species of the Braintree agilities, must have grown to a length of 18 inches. ANGELIN has figured an entire specimen of _P. Tessini_ 12 inches in length, and BARRANDE a fragment of an individual of _P. imperialis_ which must have had about the same size. Mr. G. F. MATTHEW has described a nearly entire individual of an immense _P. regina_ from the St. John beds, 15 inches long and 12 inches across the base of the cephalon, and it is claimed, with undoubted accuracy, that this is the largest undismembered specimen of a trilobite found in any country.