. The Geology of Minnesota . asizes theimportance of their various modifications to the student who busies himselfprimarily with the structure of the earth and the correlation of the early sedimen-tary deposits. To the names above given we should append those of investigatorswho have apprehended the trilobites mainly from this point of view; Conrad,Emmons, Murchison, F. and A. Roemer, Linnarsson, Dames, Billings, Whitfield. [695] 696 THE PALEONTOLOGY OF MINNESOTA. Terminology. LTerminology. As a peculiar terminology of the parts of the trilobite has been generallyadopted it will be useful to t
. The Geology of Minnesota . asizes theimportance of their various modifications to the student who busies himselfprimarily with the structure of the earth and the correlation of the early sedimen-tary deposits. To the names above given we should append those of investigatorswho have apprehended the trilobites mainly from this point of view; Conrad,Emmons, Murchison, F. and A. Roemer, Linnarsson, Dames, Billings, Whitfield. [695] 696 THE PALEONTOLOGY OF MINNESOTA. Terminology. LTerminology. As a peculiar terminology of the parts of the trilobite has been generallyadopted it will be useful to the student to recount in brief the signification of theterms employed in the following descriptions. The trilobite derives its name from the longitudinal lobation of the test intothree parallel divisions. The central division alone covers the vital and essentialorgans of the animal, the lateral portions being virtually protective integumentaryexpansions. Transversely the test is also composed of three parts, a head-plate, or. FiQ. 1—Diagrammatic figure of a trilobite. c. Cepiialon. T. TnoRAx. P. PvGimuM. 9- glabella sg. segment. an. annulation. /. frontal lobe. ag. articulating groove. pr. pleural rib. 1, 2, 3. 1st, 2d and 3d lateral lobes. pg- pleural groove. es. caudal spine l,2, 3. 1st, 2d and M lateral furrows,fixed cheeks. X. fc. free cheeks. a. axis. s. facial suture. p pleuras. e. eye. n. palpebral lobe. og. occipital groove. or. occipital ring. b. border. cephalon, C, which corresponds in a certain sense with the cephalo-thorax of the craband lobster; a median segmented portion or thorax, T, and a tail-plate, or pygidium,P. Each of these parts is in articulation with that adjoining. The central longi-tudinal lobe of the body is called, in its extent over the cephalon, the glabella, g; onthe thorax and pygidium, it is known as the axis, a. The lateral longitudinal lobes TRILOBITES. 697 Terminology.] are, on the cephalon, known as the cheeks, x\ on the thorax and pygidi
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