26 



NA TURE 



[May ii, 1882 



by Mr. Blake under the " Cont'd" diverging from this 

 and more restricted in time, having variously shaped 

 apertures, and singularly inflated, fusiform, pyriform, or 

 flask-shaped shells, are the genera Phragmoceras, Gompho- 

 ceras, Poterioaras, and Ascoceras, and placed under the 

 group " Iirflati" by the author. The other two groups of 

 the Nautiloidea — the Spirales and the Irregulares — 

 possess so great a shell curvature that they assume the 

 form of whorls, which may or may not be in contact. 

 This fact appears of sufficient importance to justify Mr. 

 Blake in regarding it as the basis for establishing the 

 group " Spiralis," in which is placed the genera. Nautilus, 

 Gyroceras, Trochilites, and Clymenia, &c, finally through 

 peculiarity of form, such as want of symmetry, or loss of, 

 or changes in curvature, are many of peculiar aspect, 

 which Mr. Blake places under the group "Irregularis',' 

 the genera contained in which are Trochoceras, Liluites, 

 Ophidioaras, and Cryptoceras. These researches have 

 led to the construction of the table of classification above 

 given. 



Prof. Blake commences his systematic description of 

 the species with the genus Orthoceras. No less than 70 

 species in this genus are described by the author, ranging 

 from the Tremadoc rocks to the uppermost Ludlow beds 

 (the Tile-stones). The species mostly abound in the 

 Bala beds, the Wenlock shales, and the two Ludlows. 

 The literature or bibliography of the species of the Ortho- 

 cerata, their descriptions, and that of the 5 sub-genera is 

 of the greatest value, and an addition to our knowledge 

 of this oldest known genus in the British rocks ; Cyrto- 

 ceras being its only associate in the Tremadoc beds. 

 The sub-divisions of the genus by Quenstedt, M'Coy, De 

 Koninck, and Barrande are given. Mr. Blake adopts 

 Barrande's views and grouping of the Orthocerata into 

 two groups : (1) the Breviconesj and (2) the Longicones. 

 The latter, which is very numerously represented, Mr. 

 Blake divides into the Anniilati, the Angulati, the 

 Limati, the Imbricati, and lastly the group Laus. In 

 this latter group is temporarily placed all species whose 

 external surface is unknown. Then follows concise but 

 clear descriptions of the five sub-genera— Aetinoceras, 

 Endoaras, Tretoceras, Conoceras, and Gonioceras. For 

 the first time we now have the 70 British species of 

 Orthocerata brought together, and most ably described 

 and figured ; 3 species belong to the group " Brevicones," 

 and 67 to the group "Longicones." Of these, 20 species 

 fall under the group Ai.nulati, 6 under the Angulati, 13 

 under the Limati, 7 under Zm bricati, and 22 in the group 

 Leves. We are now able to investigate all the known 

 species of this extensive Palaeozoic genus, and no student 

 need be at a loss to determine, either through original 

 description and drawing, or the reproduction of type 

 species, any forms that he may meet with in the Silurian 

 rocks of the British Islands. The author's plan of first 

 describing in every instance the type of the species, is of 

 extreme value, as it at once (if a known species) clears up 

 its history; this with reference to the original figure and 

 description by the author, and its reproduction in the 

 monograph, ensures and affords every chance of right 

 determination. Following the '• type " is the general de- 

 scription, then its relation to other known forms, British 

 or foreign, followed by its distribution in time or space ; 

 this plan is implicitly followed throughout the entire 



volume — it is clear, definite, and systematic. The next 

 important group described by Mr. Blake are the Cyrto- 

 ceri, numbering 22 species. These curved Cyrtoceri 

 Deshayes termed Campulites, restricting the term to 

 those species having the siphuncle on the inner side. 

 Goldfuss, however, regardless of the position of this 

 organ, named them Cyrtoceras ; Billings, De Koninck, 

 Sandberger, Giebel, and Barrande have all proposed 

 divisions for the classification of Cyrtoceras. Blake fol- 

 lows Barrande, who divides them into two series, accord- 

 ing to the position of the siphuncle: (1) the Exogastric 

 in which that organ is external ; and (2) Endogastric, in 

 which it is internal. Prof. Blake proposes a third group- 

 ing for these species, in which the siphuncle is near the 

 centre, calling it " Mediogastric." The Bala, Wenlock, 

 and Lower Ludlow beds contain most species of Cyrto- 

 ceri. The species C. precox, from the Tremadoc beds of 

 Garth, in North Wales, and from Llanerch in Pembroke- 

 shire, with Orthoceras sericeum are probably the oldest 

 forms known. 



The singular genus Gomphoceras receives much careful 

 analysis from Prof. Blake. Six of the 1 1 species are new, 

 and there appears to be good reason for their establish- 

 ment ; with one exception the species are all (10) Upper 

 Silurian, 8 of the 11 are in the Lower Ludlow beds, and 

 5 in the Wenlock Limestone. Two quarto plates are de- 

 voted to this remarkable genus. Four of the 7 species of 

 Sowerby's genus Phragmoceras are also new, and for the 

 first time figured. Like Gomphoceras this genus is chiefly 

 LTpper Silurian, the Wenlock and Ludlow strata being 

 characterised by them. Mr. Blake adds much to our 

 knowledge respecting the species of the genus Ascoceras 

 of Barrande, hitherto little known or understood ; the 

 species in Britain are confined to the Ludlow rocks. 



The group Spirales, illustrated by the genus Nautilus 

 and its sub-genera, receives ample and critical notice, 

 and shows how varied have been the views of naturalists 

 upon the affinities of this old genus, established by 

 Breynius in 1732. The value of the sub-genera in this as 

 in all the large groups is of much significance in tracing 

 the history of the obscure forms classed under the genus 

 Nautilus or Nautiloid remains in the Lower Palaeozoic 

 rocks. Five of the so-named genera — Trocholites, Cly- 

 menia, Aturia, Discites, and Nothoceras are placed under 

 the genus Nautilus as sub-genera. Mr. Blake gives 

 Quenstedt's, D'Orbigny's, and De Koninck' s classifica- 

 tion or sub-divisions, and suggests one of his own. 

 Quenstedt proposed to subdivide the genus Nautilus into 

 8 groups : (1) the Insecta, (2) Clymenia simplices, (3) 

 Clymenia angulosa, (4) the Moniliferi, (5) Bisiphites, (6) 

 Simplices, (7) Undulati, (8) Aganides. 



This and the classification by De Koninck ("Terr. 

 Carb. de Belg."), in which he partly follows Quenstedt, 

 are the only two hitherto recognised divisions of the 

 genus. The Belgian Professor places his Pateozoic 

 species under the following six heads: (1) Imperfecte, 

 (2) the Striati, (3) the Radiati, (4) Lasvigati, (5) Clymenia 

 simplices, and (6) Clymenia angulata ; four of the six 

 being those of Quenstedt. Prof. Blake proposes or 

 suggests a simpler grouping. No. 1, Simplices, illustrated 

 by the sub-genus Trocholites; 2, the Radiati, those 

 species having radiating, sigmoidal, or angular ribs ; 3, 

 the Ornati, variously ornamented, chiefly Carboniferous, 



