450 Dr. 0. Herrmann — Distribution of Graptolites. 



lites, this cannot be done until the discovery, upon one of the 

 fragments, of this organ, the presence of which proves the com- 

 pleteness of the proximal extremity, or until we find two such 

 branches held together by this dagger-shaped organ; in the former 

 case we have to do with a species of the Monograptidse ; in the 

 second with a species of one of those families which include two- 

 branched forms. 



The sicula has another significance as a classificatory element. 

 It has been shown that the further development of the hydrosoma, 

 which is commenced by the sprouting of the primordial buds, does 

 not always proceed from exactly the same spot in the sicula, but 

 that, in certain groups, which may even show agreement in their 

 other characters, it commences at different points of the margins of 

 the sicula. In the fixing of the angle of divergence between the 

 branches of the ramified Graptolites, the sicula also plays an 

 important part. 



The conditions here indicated involve a number of questions which 

 we find answered in different senses by diiferent authors, and some 

 of which have been the subjects of lively controversy, without any 

 accordant and satisfactory answer being arrived at. It therefore 

 appears to me worth while to examine some of these unsettled 

 questions in detail, and to show what views in my opinion deserve 

 the most consideration. 



In the first place we must glance briefly at the question whether 

 the Graptolites were attached by the sicula to the sea-bottom or to 

 some foreign object. Hall, who figured Graptolites with the sicula 

 as long ago as 1847, in 1865, in his great work,^ expressed the 

 opinion that some species, and especially those of the family Dicho- 

 graptidee, Lapw., in the early period of their growth, were seated 

 temporarily upon the sea-bottom or upon foreign objects. Eichter, 

 who, in 1850, figured the sicula in Thuringian forms, characterizes 

 the organ as the "foot" (Fuss) or "adherent organ" (Haftorgan), 

 names which of themselves involve the conception of its function. 

 Scharenberg,^ in 1851, writes that in many species this appendage 

 indicates a tolerably firm adhesion, but in others only a loose insertion 

 into the muddy sea-bottom. Geinitz, in 1852,^ says that the genera 

 Diplograptus and Didymograptus (Cladograptus) had "their lower 

 extremity plunged into the sand or mud." Nicholson (1872) * 

 believes that the " radicle " in some forms of the genus Didymo- 

 graptus, M'Coy, served as an adherent organ, but that other genera, 

 such as Monograptus, Gein., and Coenograptus, Hall, were not attached 

 by that organ. 



More recently an opinion has made much way that all Graptolites 

 provided with a sicula inhabited the sea as non-attached organisms, 

 and that the discovery of the sicula on imperfectly known forms of 



1 Figures and Descriptions of Canadian Organic Remains, Dec. ii., Graptolites of 

 the Quebec Group, Montreal, 1865. 



2 Ueber Graptolithen, etc., Breslau, 1851. 



2 Die Vcrsteinerungen der Grauwackenformation in Sachsen: I. Graptolithen, p. 17. 

 * Monograph of the British Graptolitidse, p. 63. 



