clxii BRITISH GRAPTOLITES. 



attention is very properly called throughout to the memoirs and conclusions of 

 Dr. Gurley on American Graptolites. Several of his MS. diagnoses, figures, and 

 descriptions are included, and their sources acknowledged in the body of the work. 



The General Section of the volume is illustrated by tables of local distribu- 

 tion, zonal range, and classification. The earlier and later nomenclatures of the 

 Graptolite-bearing formations are given and discussed. Five successive Graptolite 

 zones are distinguished in the Upper Ordovician, namely, those of (1) Nemagraptus 

 gracilis, (2) Diplograptus amplewicaulis, (3) Olossograptus quadrimucronatus, 

 (4) Diplograptus peosta, (5) Dicellograptus complanatus, embracing the American 

 strata ranging from the base of the Black River Formation to the top of the New- 

 York Ordovician. 



The notes on morphology, etc., given in the first volume are here supplemented 

 and extended. The known facts and varied views respecting spines, basal discs, 

 vesicles, virgula, nema, retiolite-structure, etc., are adduced and discussed, and 

 illustrated by abundant text-figures, and several new observations respecting the 

 polypary and thecse in the Graptoloidea are brought forward. Attention ought 

 also to be called to Ruedemann's notes, descriptions, and figures of the so-called 

 genera which he classes together under the title of ' Genera incertse sedis.' Of 

 these, the most important constitute the group Gorijnoides of Nicholson, which 

 Hopkinson and Lapworth (1875) erected into a distinct family under the title of 

 Corynograptidse. The author changes the name to Corynoidse, and gives several 

 instructive figures of the New York forms. These he identifies with the known 

 British species, but recognises several varieties. 



The Descriptive Section of the volume is devoted to the diagnoses and figures 

 of the Graptolite forms themselves. One hundred and seventeen species are 

 recognised by the author, of which fifty-one are assigned to the Dendroidea 

 and sixty-six to the Graptoloidea. Three new genera, viz. Ptiograptus and 

 Mastiograptus, are classed among the Dendroidea. The new species of Den- 

 droidea include Bendrograptiis rectus, Ptiograptus Poctai, P. Hartnageli, Odonta- 

 culis hepaticus, Ptiograptus percorrugatus, Desmograptus tenuiramosus, I), cadens, 

 D. Vandelooi, Cactograptus crassus, Palseodictyota anastomotica, P. Clintonensis, 

 Mastigograptus circinalis, together with the following MS. forms of Dr. Gurley: 

 Dictyonema polymorphum, D. Leroyense, D. Areyi, 1). megadictyon, IK 

 perradiatum. 



The new forms of Graptoloidea embrace Azyograptus simplex, Syndograptus 

 pecten, Dicellograptus mensurans, D. Smitbi, ( '. Mississippiensis, G. modestus, 

 Gyrtograptus Ulrichi, and the following MS. species of Lapworth : Azyograptus 

 Walcotti, Nenmgraptus exilis, Dicranograptus Gurleyi. 



This second volume of Ruedemann's Monograph is clearly the work of an en- 

 thusiast in the subject ; but one who nowhere poses as an authority, or disguises 

 either the defects in our knowledge or the inevitability of diverse interpretations. 



