Dr. H. A. Nicholson on new Species of GraptoUtes. 231 



podia, as has been done by Stimpson, The gastric region is 

 narrow and projects far forward as in the Maioids. The ex- 

 pansions 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 verj much the form of 

 that of Gryptopodia. 



XXVII. — On some neio Species of Grap>tolites. 

 By Henry Alleyne Nicholson, M.D., D.Sc, M.A., F.G.S.* 



[Plate XL] 



Having recently discovered a considerable number of new 

 forms of Graptolites, I purpose in the following communica- 

 tion giving a short diagnosis of the more remarkable ones 

 amongst them, reserving a more detailed description for an- 

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

 described from the Skiddaw Slates (Quart. Journ. Geol. Soc. 

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

 I have also detected Diplograpsus hicornis, Hall, and Phyllo- 

 yrapsus Anna, Hall, thus raising the total number of Grapto- 

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

 tolitic fauna 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. 



Trigonogeapsus, gen. nov. PI. XI. fig. 6. 



Gen. cliar. Frond simple, diprionidian, rapidly tapering 

 towards the base, and having perfectly plain lateral margins 

 without denticles. Cell-partitions alternating with one an- 

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

 A common canal is probably present, in which case the axis 

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



I have been compelled to found this genus for the reception 

 of a single remarkable form v/hich I have recently found in 

 the Skiddaw Slates, and which differs considerably in struc- 

 ture from both Betiolites and Diplograpsus. As defined by 

 Barrande, Retiolites is distinguished 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 apj)ly in their entirety is the 



* Communicated by the Author, having been read before Section 

 of the British Association, at Exeter. 



