364 SCIENCE PROGRESS. 



gibberulus, and certainly occurs in many other forms of 

 Dichograptidce. Another filiform appendage which might 

 be spoken of as the false virgula " originates as a result of 

 growth within the apertural end of the sicula at some 

 distance from the initial portion. This later structure 

 stands evidently in no relation whatever to the real 

 virgula, but may be regarded as an apertural spine." The 

 significance of these filiform processes has not yet been 

 fully explained, but the possession of a true virgula must in 

 future be omitted from diagnoses of the characters of the sub- 

 class or sub-order of the graptolites. Holm's researches 

 fully confirm Tullberg's inference that Phyllograptus belongs 

 to the family Dichograptidce, and the family Phyllograptidcz 

 must now be abandoned. Another interesting point bear- 

 ing upon classification is the position from which the bud 

 grows out of the sicula. " In Phyllograptiis it is situated 

 quite close to the apex of the sicula, in Tetragraptus 

 Bigs by i Hall probably slightly lower down, in Didymograptus 

 miniUus Tornq. somewhat below the middle of the 

 sicula, in Didymograptus gracilis Tornq. Mut. still nearer 

 the aperture ; but in Didymograptus gibberulus Nich. the 

 position is almost the same as in Pliyllograptus." The 

 reference of the genus Azygograptus to the Nemagraptidce 

 on account of the stipe being developed from the central 

 part of the sicula on one side is therefore unnecessary, and 

 the general characters of Azygograptus leave no doubt 

 that it belongs to the Dichograptidce ; indeed Holm in the 

 paper under consideration describes a form which is possibly 

 intermediate between Didymograptus and Azygograptus. 



The association of a number of graptolites of the same 

 species in a fairly symmetrical manner has long been 

 known. James Hall in plate xiv. of his classic work on 

 graptolites (12) figures a diprionidian graptolite under the 

 name of Retiograptus teutaculatus, and in figure 9 is "an 

 illustration of a compound form of the genus," possessing 

 nearly twenty diprionidian stipes diverging from a common 

 centre. James Dairon (13) also figures specimens of 

 Monograptus occurring in partly symmetrical tufts, and 

 remarks : " I am now thoroughly convinced that many, if 



