222 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



simplicit}^ of form in these cylindi-ical shells being accompanied by a correspond- 

 ingly simple form in the septa. It is noticeable that Hyatt makes no direct reference 

 to the septation in defining his sub-orders, families, and genera of the Nautiloidea 

 in Eastman's ' Translation,' but depends rather npon the nature of the septal 

 necks and the siphuncle and its contents, if any, taking into account likewise 

 characteristic ornamentation . 



The arrangement of the remaining groups of the Nautiloidea (exclusive of the 

 Actinoceratidae, Cyrtoceratidse, and Poterioceratidae) follows in the main that of 

 Hyatt's " Carboniferous Cephalopods," contributed to the ' Geology of Texas, 

 Fourth Annual Rep.' (1892), Avith such modifications as it became necessai-y to 

 make in the presence of the new material available. 



For the Ammonoidea, here represented hj the Goniatites, Hyatt's widely recog- 

 nised classification has been adopted, though in the case of the largest and most 

 imi)ortant group, the Glyphioceratidse, some changes have been introduced. Under 

 his original description of Glyphiocevas Hyatt divided the genus into two sections 

 which he characterised, and to which he allotted certain species. To these unnamed 

 sections I have given distinctive names as sub-genera, and following Perrin Smith, 

 have resuscitated Muensteroceras, also as a siib-genus, taking the suture-line in each 

 case as the principal distinguishing feature (Synopsis of Families, Genera, etc., p. 219). 



The retention of Gastrioceras as an indej^endent geniis, rather than the 

 merging of it in Glypldoceras, as suggested by Karpinsky,^ is held by Perrin Smith 

 to be justified by the fact that Gastrioceras being a later branch than Glijphioceras, 

 phylogenetic studies arc facilitated by their separation, while there is no difficulty 

 in distinguishing typical members of each group. Gastrioceras is therefore main- 

 tained in accordance with this view. 



The most cursory survey of the mateiial at present collected and recorded shows 

 plainly what a rich molluscan fauna is contained in the rocks of the Carboniferous 

 System spread over a great part of Ireland. It is a safe prediction that with more 

 workers in the field much additional material might be gathered in, thereby greatly 

 facilitating those studies which may lead to the most important results in all that 

 relates to the phylogeny of the Cephalopoda, and the important biological and 

 favuial questions they help to elucidate ; for, as it has been truly stated, " the 

 Cephalopoda alone, of all animals, preserve in the individual a complete record of 

 their larval and embryonic history, the protoconch and early chambers being 

 enveloped and protected by the latter stages of the shell." * Hence the great 

 importance that nmst be attached to the collection of many individuals of the same 

 sjjecies to supply the means of carrying out such embryological work as has already 



1 ' Proc. CalifonuLi Acad. Sci.,' third ser., Grcology, vol. i, No. 3, p. 105, 1897. 



2 ' Mi'iii. Acad. Imp. Sci. St. Pctersboury,' vol. xxxvii, p. 48, 1889. 



■' J. Pcrriu Smith, iu ' Proc. Amor. Phil. Soc.,' vol. xxxv, 1896, p. 264. 



