MONOGRAPTUS. 359 



Famihj MONOGRAPTID^, Lnjnvnrfh. 

 1873. Monogra])tidiv, Lapwortli, Geol. Mag-., vol. x, table 1, p. 555. 



Unilateral Graptoloidea, poljpary simple or compound, straight or curved. 

 Tliecae varied in form, growing upward in a single linear series along the line of 

 the virgula. 



In the forms belonging to this family the first theca is budded from a A^ariable 

 point along the length of the sicula and grows at once upward and outward ; 

 all the succeeding thecse follow the same direction. 



This type of development, as we have already pointed out (p. 347), has been 

 anticipated in the Dimorphograptidte ; but in that family the polypary is uniserial 

 in the proximal portion and biserial in the distal portion, whereas in the Mono- 

 graptidse it is uniserial throughout. 



The family of the Monograptidfe as originally founded, was regarded as 

 embracing three genera: Monograptus, Geinitz, restricted, Rastrites, Barrande, and 

 Gyrtograptus, Carruthers. Ci/rfograpfus included all the branching species ; lin^trUes 

 those unbranching forms in which the theca3 had the appearance of being isolate ; 

 and Monograptus the remaining unbranching and more typical forms of the family. 



The branching nature of the polypary in Cyrtograptiis is perhaps sufficiently 

 distinctive to entitle the group so named to generic rank; but it is doubtful if the 

 peculiarities of the thecas in the forms united under Rastrites are of greater signi- 

 ficance than those characteristic of the various sub-groups in Monograptus itself, 

 and Rastrites is here regarded as a sub-g-enus. 



Genus MONOGRAPTUS, aeinit^, restricted. 

 1852. Monogra^tns, Geinitz, Die Graptolithen, p. 32. 



Fohjpary simple. 



Tliecse cylindrical, conical, or somewhat flattened tubes; in contact, overlapping, 



or becoming more or less isolate ; walls straight or curved ; apertural 



margins variable in form, plain or ornamented. 



The polypary in Moyxograptiis presents many variations in its general features, 



apart from considerations of length and breadth. In several species the polypary 



is straight {Monog. jaciilum), but in the majority it is distinctly curved. The 



curvature may be (1) ventral, the polypary being bent forward in the direction of 



the ventral margin and bearing the thecse upon the inner side of the curve {Monog. 



hohemicus) ; or (2) dorsal, the polypary being curved backward and bearing the 



48 



