GRAPTOLITES. 41 
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. 
Mr. 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 is the typical form 
of Graptolithus of Linneeus. 
The genus Cladograptus* is also proposed by Mr. Geinitz, to include 
the species G. ramosus and G. furcatus, Hall, G. Murchisoni, Beck, 
G. serra, Brong., G. Forchhammeri, Geinitz, and G. sextans and G.. serra- 
tulus, Hall. At the same time the British paleeontologists, adopting the 
name Didymograptus, McCoy, 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 gemelle” of 
Bronn, who included under that term the G. geminus, Hisinger, and 
G. Murchisoni, Beck, which are by no means nearly related to G. ramosus 
or G. furcatus. The first-named two species, which were the earliest 
known of that character, and regarded as the typical forms of Didymo- 
graptus, are similar to G. bifidus and G. extenuatus of this memoir, 
which differ from the other species on plates i, ii, and ii, only in the 
lesser divergence of the stipes. 
Very recently Mr. Salter has proposed a further subdivision of the 
graptolites under the name Jetragraptus, ‘a kind of double Didymograp- 
tus,’ of which G. bryonoides is made the typical species ; and G. quad- 
ribrachiatus is referred to the same genus. He also proposes Dichograp- 
tus for those having the “fronds repeatedly dichotomous from a short 
basal stipe mto eight, sixteen, twenty-four, or more branches, each with 
a single row of cells.”’ “ But the main character which distinguishes 
Dichograptus is the presence of a corneous plate | which envelopes 
all the lower part of the branches, and which is not known in any other 
genus of the group; it has not indeed been seen in more than two or 
three species of Dichograptus, but it may not in all cases have been pre- 
served.’ 
These subdivisions may be of some value when the entire frond and all 
its appendages are preserved, but unfortunately this is rarely so; and 
when we have but fragments of the stipes or branches, there is no force 
* CuapoGRApsus, Geinitz. Syn. Graptolithus auctorum ; species gemelle, Bronn. (Die 
Versteinerungen der Grauwacken formation in Sachsen, etc. Heft. i, Graptolithen, p.29.) 
Monocrapsvs, id., ibid., p. 42. Syn. Monoprion et Rastrites, Barrande; Graptolithus, 
Suess. 
{ First discovered in the graptolites of the Quebec group at Point Lévis. 
t Quarterly Journal of the Geological Society, vol. xix, p. 136. 
