Dr. H. A. Nicholson oh new Sj)ecies of GrcqAoUtes. 231 



2)0(Im, as lias Leon done by Stinipson. The gastric rco;ion is 

 narrow and j^rojects far forward as in the Maioids. The ex- 

 ]xuisions on the sides of the carapax, which give it a Cancroid 

 form, are thin, and contain none of the internal organs ; and 

 their removal would give the carapax very much tlie form of 

 that of Crf/ptojjodia. 



XXYII. — On some new Species of Graptoh'tes. 

 By Henky Allkyne Nicholson, M.D., i).Sc., M.A., F.G.S.* 



[Plate XI.] 



Havixo recently discovered a considerable number of new 

 forms of Graptolites, I purpose in the following connnunica- 

 tion giving a short diagnosis of the more remarkable ones 

 amongst them, reserving a more detailed descri])tion for an- 

 other occasion. To the twenty-fonr species which I formerly 

 described from the Skiddaw Slates (Quart. Journ. Geol. 8oc. 

 vol, xxiv. p. 125) I have now to add seven new species ; and 

 I have also detected Diplogrnpsiis hicorm's, Hall, and P/if/Uo- 

 (/rapsus Anna, Hall, thus raising the total number of Grapto- 

 lites from this formation to thirty-three. To the rich Grap- 

 tolitic tauna of the mudstones of the Coniston series I have 

 three new forms to add, making with those I have previously 

 described a total of twenty-seven species (see Quart. Journ. 

 Geol. Soc. vol. xxiv. p. 521). Finally, I have a few new spe- 

 cies from the Upper Llandeilo rocks of Dumfriesshire. 



Trioonograpsus, gen. nov. PI. XI. fig. G. 



Gen. char. Frond simple, diprlonidian, nipidly tapering 

 towards the base, and having ])erfectly plain lateral margins 

 without denlicles. ('ell-])artitions alternating with one an- 

 other, and springing from an undulating or zigzag solid axis. 

 A common canal is ])rol)ably present, in which case the axis 

 must be excentric ; but the evidence on this point is incomplete. 



I have been compelled to found this genus for the reception 

 of a single remarkable form which I have recently found in 

 the Skiddaw Slates, and which differs enusiderably in struc- 

 ture from both Iicfioh'tes ami I)ijili)(jrapsiis. As detined by 

 Barrande, lietioUtrs is distinguishccl by the triangular shape 

 of the frond on transverse section, by the absence of a solid 

 axis, and by a characteristic punctation of the test. The only 

 form to which these characters ap})ly in their entirety is the 



• Communicated by the Author, having been read before Section C 

 of the British Association, at Exeter. 



