STUDY OF THE GRAPTOLITES. 213 



Diplograptus rectangularis of M'Coy* is of the same type, as also figs. 1, 

 5, 10, 11, 12, etc., Tab. ii, of Geinitz [Graptolitheii) ; and I conceive 

 that many of the scalariform specimens belong to species of this character. 



The Graptolithus ramosits has usually been arranged by authors under 

 Diplograptus ; the lower part of tlie stipe having a double range of cellules, 

 on the outer margin of each division, as already described; and a simple 

 explanation of this condition has been offered by supposing that the solid 

 axis has been divided after the death of the zoophyte. This, however, 

 will scarcely afford a satisfactory argument when we find that all the 

 specimens are in the same condition; that usually the division begins at a 

 uniform distance from the base; and that when entire, the divided portion 

 much exceeds the simple undivided part of the stipe. Moreover, the 

 species is recognized in tliis condition in the Hudson-river formation in 

 Canada, and has likewise been recognized in Great Britain ; while a similar 

 or identical form has been shown by Prof, M'CoY to occur in Australia. 

 We must therefore seek some other than an accidental cause for the expla- 

 nati on of this uniform bifurcation ofthe stipes of that species. In the 

 meantime, it appears to me highly proper to suggest its separation from 

 Diplograptus. , 



On farther comparison, we shall find that G. ramosus is not quite alone 

 in its peculiar characters. In G. furcatus there are a few cellules at the 

 base of a simple stipe below its bifurcation ; and in G. sextans, the lower 

 part of the stipe is simple, the division taking place above the first cellule ; 

 but in entire individuals the division is never from the initial point, as we 

 see it in G. hijidus and G. ?iitidus. 



Now these first named species, as well as G. raniosits, have cellules of a 

 peculiar form ; and looking still farther, we find a similar form of cellule in 

 G. forclihammeri, Geinitz, and G. divaricatus, Hall, two species which 

 are divided from the base, having a single range of cellules upon the outer 

 sides of the stipe. I believe it will be found, moreover, that all the 

 graptolites with cellules on the lower side of the stipes (in reference to the 

 initial point or radicle) have these parts of the same form as in G. ramoaus, 

 and very unlike the G. pristis and allied species. Nor are the cellules on 

 the simple or divided portions of the same stipe, or on those whicli are 

 entirely divided, and upon the lower side, at all like the cellules of G. priodon^ 

 G. gejninus, G. ??iurchisoni, or any of the allied forms illustrated in this 

 memoir to which the term Didymograptus has been applied ; nor can they 

 be properly united with them. The form of the cellules is always suffi- 

 ciently distinctive, even in fragments of the. stipes ; and this feature, 

 together with the mode of development or growth, seems to me sufficient 

 to sustain a generic distinction. 



The Genus Retiolites is described by M.Barrande as having no central 

 solid axis, but with a single internal canal occupying the median portion 



* British Palaeozoic Fossils, page 8, pi. xiii, figs. 8, 9, and 10. 



