of the Genus Ptilograpsus in Britain. 239 



with specimens of a new species of Ptilograpsus, which I pur- 

 pose to describe briefly under the name of P. anglicus. The 

 generic characters of Ptilograpsus consist in the possession of 

 a branching plant-like frond, the branches and branchlets 

 plumose. The pinnules spring alternately from opposite sides 

 of both the primary and secondary divisions of the frond, and 

 are celluliferous on one side only. The base of the frond is 

 not known, the probability, however, being that the organism 

 was fixed. 



As pointed out by Hall, Ptilograpsus closely resembles the 

 v^iodiem Plumularia ; and, as far as its characters are yet known, 

 there is perhaps no really important point of difference. Cer- 

 tainly the resemblance to such forms as Plumularia cristata 

 and P. myriophyllum, the first especially, is most striking, 

 and must be more than merely mimetic. Like Dicfyonema, 

 Dendrograp)sus, and Callograpsus (all genuine Graptolites), 

 Ptilograpsus was probably permanently attached, though in 

 none of these genera has the commencement of the " liydro- 

 caulus " been yet detected. Another point in which Ptilo- 

 grapsxis agrees with the above-mentioned genera and differs 

 from the great majority of Graptolites is in the apparent ab- 

 sence of the " solid axis"*, the individual branchlets consisting 

 simply of cellules or " hydro thec£e " springing from a common 

 canal or " coenosarc." By this absence of the solid axis, of 

 all Graptolitic structm'es the most anomalous, Ptilograpsus 

 manifestly approaches very closely to the Sertularian type, 

 though not more closely, perhaps, than do Callograpsus and 

 Dendrograpsus. Dictyonema, again, though certainly belong- 

 ing to the same natural subgroup of the Graptolitidas as the 

 above three genera, has a fresh structure superadded in the 

 shape of transverse dissepiments connecting together the dif- 

 ferent branches which constitute the frond. 



Ptilograpsus anglicus, spec. nov. 

 Spec. char. Frond slender and branching, all the branches, 

 large and small, being provided with pinnule, which spring 

 alternately from opposite sides, and bear angular cellules on 

 one face. Pinnulai from twenty to twenty-eight in an inch, 

 their length varying from two to three twentieths of an inch. 



* The " solid axis " has usually been supposed to he an essential element 

 in the structure of every Graptolite, the genus Retiolites alone excepted. 

 In common with the great majority of wiiters on the subject, this belief 

 was shared by myself, and I did not believe that even the above-mentioned 

 exception would be found to hold good. Recent investigations, however, 

 into this particular point have led me to the opinion that the axis is not 

 so constantly present as has been generally thought, that it is certainly 

 absent in the genera I have spoken of, and probably absent in others. 



