208 TWENTIETH REPORT ON THE STATE CABINET. 



the cellules. From these fragments, however, we have derived the generic 

 characters ; while the modifications in form, and the order and relations of 

 cellules, have furnished means of specific distinctions in the greater pro- 

 portion of those described. 



In maintaining the generic term Graptolithus for the forms which have 

 the nearest relations with those to which the term was originally applied 

 by LiNN^us, M. Barrande has proposed two sub-genera, characterized 

 by the presence of a single series, or of two parallel series of cellules, 

 under the names of Monoprion and Diprion. The latter term having been 

 applied to a genus of insects, the name Diplograptus * of McCoy has 

 generally been adopted. 



The distinction indicated would at one time have expressed a character 

 perfectly trenchant; but the discovery of such forms as G. ramosusf and 

 G.furcatus, shows the occurrence of both a single and a double series of 

 cellules upon the same stipe, or, more properly, shows the basal portion 

 consisting of a stipe, with two parallel ranges of cellules. The stipe, 

 dividing- at some distance above its origin, is continued as two simple stipes, 

 each with a single range of cellules. These cellules are on the outer 

 margin, and are a continuation without interruption from those of the 

 lower part of the stipe. Including these therefore in the same group with 

 G. pristis, the subdivisions indicated would have less value for the purposes 

 of study ; but I believe these latter forms may be separated on other 

 grounds, as will be shown farther on ; so that with our present knowledge 

 we may still recognize Diprion, = Diplograptus, as a well-marked and 

 clearly-defined sub-generic group of the Graptolithus proper, having such 

 forms as G. pristis among the typical species. 



M. Geinitz has more recently proposed the name Monograptus to 

 include Monoprion and Rastrites of Barrande ; placing under this genus, 

 as his typical species, G. Sagittarius of Hisinger, which has usually 

 been regarded as the typical form of Graptolithus of Ltnn/EUS. 



The genus Cladograplus t is also proposed by M. Geinitz, to include 

 the species G.ramosus and G./zzrca^ws, Hall; G. murchisoni, Beck; 

 G. serra, Brongniart ; G. forchhammeri, Geinitz ; and G. sextans and 

 G. serratulus, Hall. At the same time the British palaeontologists, 

 adopting the name Didymograptus, M'CoY, place under that genus G. 

 murchisoni, Beck; G. caduceus, Salter; G. sextans, Hall; G. geminus, 

 Hisinger; G. hirundo, Salter, and other similar forms. Those which 

 are made the typical forms of the genus by Geinitz are the " species 

 gemellcR^'' of Bronn, who included under that term the G. geminus, Hi- 



* In the genera proposed by myself, I have chosen the termination f^raptus instead of 

 grapsus, since the latter termination is in use in the nomenclature of Crustacea. 



f The subdivision of this species beyond the first bifurcation, represented in the Paige- 

 ontology of New York, Vol. i, pi. Ixxiii, fig. 3, is erroneous; the specimen consists of 

 two individuals, the base of one being placed directly in the axil of the other. 



J Cladograpsus, Geinitz. Syn. Graptolithus auctorum; species gemellce, Bronn (Die 

 Versteinerungen der Grauwacken formation in Sachsen, etc., Heft i, Graptolithen, p. 29). 

 Monograpsus, Id. ibid. p. 42. Syn. Monoprion et Rastrites, Barrande; Graptolithus, 

 SuESS. Not Cladograptus, Caruuthbrs. See supplementary note. 



