Reviews. — Prof. Nicholsons British Graptolites. 231 



affinities of the graptolites put forward in Eicliter's last paper on 

 this subject (1871). But whether the true graptolites, the Ehabdo- 

 phora of Allman, should form a distinct order of the class Hydrozoa, 

 or a sub-order of the order Hydroida, still remains for determina- 

 tion. In this memoir they are considered to form a distinct order, 

 or rather "sub-class " of the Hydrozoa, and under the name Grapto- 

 litidce are grouped together the Ehabdophora, the Dendroidea, and 

 a few genera of doubtful affinity. 



The next chapter comprises a brief summary of the present state 

 of our knowledge of the geological distribution of the Graptolites 

 and their allies. The author divides the Silurian epoch, to which 

 these fossils are almost exclusively confined, into three distinct 

 periods : — 1. The Skiddaw and Quebec period. 2. The Llandeilo 

 and Caradoc period. 3. The Upper Silurian period. If we include 

 the Lower Llandeilo or Arenig group in the first period (its proper 

 place), and eliminate from this period the species Dicranograptus 

 ramosus, which really begins in the true Llandeilo and not in the 

 Arenig rocks, we shall find that out of the ninety British species 

 here enumerated, but three pass from the Skiddaw and Quebec, or 

 Arenig period, to the Llandeilo and Caradoc period. From the 

 Lower to the Upper Silurian rocks the well-known species Grapto- 

 lithus priodon and G. colonus alone pass. 



Recent researches tend to show that the Ehabdophora are even 

 more restricted in their range in time than appears from the table 

 given in this chapter. We refer especially to the researches of 

 Lapworth in the Lower Silurian rocks of the south of Scotland. 

 The Dendroidea, on the other hand, will probably ultimately be 

 found to have a more extensive range than hitherto supposed. 



In the ninth and concluding chapter the genera of the Grapto- 

 litidae are described. They are grouped into five " sections," named 

 respectively, Monoprionidae, DiprionidEe, Tetraprionidee, Dendroidea, 

 and Incerte Sedis. The sequence in which the genera of the 

 Monoprionidge are described shows that the author does not clearly 

 comprehend the affinities of the different forms ; and from the sup- 

 pression of the genus Dicellograptus, which constitutes with Dicrano- 

 graptus the section or family MonodiprionidEe, it would appear that 

 he has failed to recognize the primitive morphological types 'upon 

 which the several generic forms are constructed. 



The few defects we have endeavoured to point out are of slight 

 consequence compared to the large amount of valuable matter which 

 is here brought before us. The present part of Prof. Nicholson's 

 Monograph forms a complete introduction to the study of the British 

 graptolites, and being written in the free though concise style 

 which characterizes all the author's works, being admirably printed, 

 and profusely illustrated with well-executed woodcuts, will be 

 read with pleasure by all who take an interest in Silurian 

 palaeontology. It is undoubtedly the most important memoir on 

 the graptolites which has appeared since the publication of Mr. 

 Carruthers's Enumeration of the British Species (Geol. Mag., Vol. 

 V. 1868), and when completed will, we doubt not, fully equal, 

 if not surpass. Prof. Hall's splendid Monograph on the Graptolites 

 of the Quebec Group. J. H. 



