. Annual report. New York State Museum; Science; Science. GRAPTOLITES OF NEW YORK, PART 2 449 constancy of its differential characters in all specimens from the same horizon leave no doubt that we have a mature though dwarfed form before us. Family monograptidae Lapworth monoqraptus Geinitz, em. Jaekel et Freeh While the genus Monograptus is so profusely represented in the Siluric of Europe that not only a great number of species have been distin- guished but its distribution has also been the means of the elaboration of a most refined system of Siluric horizons, North America has, besides a f
. Annual report. New York State Museum; Science; Science. GRAPTOLITES OF NEW YORK, PART 2 449 constancy of its differential characters in all specimens from the same horizon leave no doubt that we have a mature though dwarfed form before us. Family monograptidae Lapworth monoqraptus Geinitz, em. Jaekel et Freeh While the genus Monograptus is so profusely represented in the Siluric of Europe that not only a great number of species have been distin- guished but its distribution has also been the means of the elaboration of a most refined system of Siluric horizons, North America has, besides a form in the arctic North, yielded but two species, one in the Clinton beds of New York and one in the Siluric of Maine, and both of these are hardly more than mutations of the most common and best known European species, M. p r i o d o n Bronn. We can, therefore, restrict ourselves to a consideration of the group of Monograpti of which M . priodon is the representative. The genus Monograptus, as originally conceived (Lomatoceras Bronn, Monoprion Barrande and Grapto- lithus of some authors) has been derived through forms of Dimorphograptus from Diplograptus and Climacog- raptus, by the reduction of the biserial arrangement of their thecae to a uniserial one. In correspondence to 423 J 424 Fig. 423, 424 Copies of this origin of the genus the sicula occupies the most distal giTp0suVge^Tg0aV^0an0d r1 ... ,, 1 . Monograpsns rectus, point 01 the rhabdosome and the thecae grow in a reversed respectively direction, climbing up along the nemacaulus as in Diplograptus and Clima- cograptus. This position of the sicula and the growth .direction of the first theca (first downward and then upward) are well shown in some of our Clinton specimens [see fig. 428]. The form of the thecae was extremely diverse in the genus Mono- graptus as originally conceived and has led to the distinction of several genera. Those with the thecae of a Climacograptus have been united by Freeh [1897, ] under Mo
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