556 C. Lapworth — On British GraptoUtes. 



contrary, the families are constituted by assemblages of species, 

 linked together by a large community of morphological characters, 

 and grouped around typical genera. The most characteristic genus 

 in all cases furnishes the name for the family. The new scheme 

 therefore _ admits of modification in matters of detail, or of the 

 intercalation of new families, which the exigencies of science will 

 certainly demand, in proportion as future research throws light upon 

 doubtful points of structure, or furnishes us with certain evidence of 

 the methods of multiplication and reproduction, among these ancient 

 creatures. 



The arrangement of the monoprionidian forms in the present 

 scheme is, upon the whole, the natural one, and this view of their 

 relationships is strikingly confirmed by the known geological distri- 

 bution of the genera constituting the several " families." The latter 

 are well circumscribed, and the slightest fragment of the branch of 

 a monoprionidian species can be referred at a glance to its proper 

 family. It was with great pleasure that I learnt from Mr. Hopkin- 

 son at the beginning of the present year, that he had independently 

 arrived at a similar classification of these uniserial forms. To 

 this eminently acute observer must also be assigned the credit of 

 being the first in acknowledging the propriety and value of Professor 

 Hall's separation of Didymograptus and Bicellograptus, and in carrying 

 it out to its proper limits. His views upon these points are adopted 

 in the Table. He was also the first to call attention to the fact that 

 Leptograjitus flaccidus (Hall sp.) could rightly be referred to neither 

 of the foregoing genera, but more probably belonged to the genus 

 Nemagraptns of Engimons.^ The importance of his clear recognition 

 of this circumstance, which may be said virtually to contain within 

 itself the clue to the differentiation of the well-marked group of the 

 NemagraptidiB, I have in some degree endeavoured to acknowledge, 

 by relinquishing my proposed title for this family, in favour of the 

 MS. name applied to it by Mr. Hopkinson. 



The classification of the Graptolites with two ranges of thecal 

 {DiplograptidcB), although in my opinion the best possible in the 

 actual state of our knowledge, is to be regarded as confessedly 

 temporary and provisional. Not only are the limits of the major 

 divisions badly defined at present, but the minor grouping we are 

 compelled to adopt is essentially artificial. Indeed it may be con- 

 sidered certain that future research will demonstrate the necessity 

 for a very different distribution of many of these forms. 



All that is attempted in this department is roughly to prepare the 

 way for the next and future advance in the proper classification of these 

 species. This will probably consist in the suppression of the family 

 Phyllograptidm, whose single genus may have to be included among 

 the piplograptidcB. From the latter it may ultimately be necessary 

 to eliminate the genus Climacograptus, and to place it, together with 

 Lasiograptus, near the family of the Dicranograptidce. There is also 

 evidence in su]3port of the view that the more typical species of 



' Geol. Mag., Vol. VIII., p. 64. 



