1 BRITISH GRAPTOLITES. 



with the same number of stipes do not possess one. He does not accept Geinitz's 

 genus Cladograpsus, and agrees with Bronn in rejecting Geinitz's Nereograpsus 

 and Emmon's Nemapodia, which are probably worm tracks. Emmon's genera 

 Glossograpsus and Nemagra/psus are rejected by Hall, but he observes that Emmon's 

 Staurograpsus, "if accurately represented in the figure, merits generic distinction." 



He retains the genus Diplograpsus of M'Coy. not on account of its form, but on 

 account of the shape and arrangement of the cellules, which are the same as those 

 in the various species of Grapfolithus (Didymograptus) described by himself. From 

 this genus Diplograpsus, however, as previously accepted, Hall separates under the 

 name Climacograptus those double forms, the cell-apertures of which are "excavated 

 in the margins of the stipes, without tubular or cup-form extension." He gives a 

 very careful and detailed description of the structure of this new genus, illustrated 

 by excellent figures. He regards his G. bicornis as the type, but includes also 

 Pr. teretiusculus, His., and D. rectangularis, M'Coy, in the same genus; and he 

 conceives that many if not all of the scalariform specimens figured by previous 

 authors belong to species of this character. 



Hall also recognises the fact that the cells in such forms as Gr. ramosus and 

 Gr. Forchammeri are similar in structure to those of Climacograptus, and he pro- 

 poses the sub-generic title of Dicranogr aphis to include all such species. 



Barrande's genera Bastrites and Retiolites are retained, but Hall differs from 

 Barrande in believing that in the latter genus the axes are two in number — on one 

 side a straight cylindrical solid axis, and on the opposite side an undulating or 

 zigzag filiform axis. The structure of Retiolites, so far as Hall was able to work it 

 out from the material at his disposal, is given in illustrative figures. 



As regards his own genus Retiograptus, Hall supposes that " the two sides of 

 the stipes are very unlike each other in form and external characters, as is the 

 case in Retiolites." 



The four genera of Dendroid forms, viz. Dendrograptus, Oallograptus, Dictyonema, 

 and Ptilograptus, are placed by him in the family of the Graptolitidas, but he 

 suggests that when further information has been obtained as to their structure, it 

 may be necessary to separate them from this family. In Dictyonema he is unable 

 to recognise a solid axis, but he believes that it existed in Ptilograptus. The 

 peculiar genera Inocaulis, Buthograptus, and Oldhamia lie holds can only be doubt- 

 fully classed among the Graptolitidse. 



It may be noted that Hall here first adopts the termination " graptus " instead 

 of " grapsus " for all his new genera, " since the latter is used in description of 

 Crustacea." This modification of the earlier terminology may be said to be 

 universally adopted at the present day. 



Description of Species. — The following large number of species are described 

 and figured by Hall in this work (the generic names in brackets are those 

 employed at the present day) : — 





