NATURE 



2 5 



THURSDAY, MAY u, 1SS2 



BRITISH FOSSIL CEPHALOPODS 

 A Monograph of the British Fossil Cephalopoda. Part I. 

 Introduction and Silurian Species. By J. F. Blake, 

 Esq., M.A., F.G.S., Professor of Natural Science in 

 University College, Nottingham. (London : J. Van 

 Voorst, 1882.) 



FOR the first time has just appeared Part I. of a 

 monograph upon the British Palaeozoic Tetra- 

 branchiate Cephalopoda, and important as this group of 

 Mollusca has ever been regarded by all palaeontologists 

 and badly as such has been wanted by all students of 

 British Palaeozoic geology, no one has hitherto attempted 

 any history of this group for Britain. Barrande has 

 elaborately done so for Bohemia and De Koninck for 

 Belgium, both have extensively written upon the older 

 Cephalopoda [Cambrian, Silurian, Devonian, and Car- 

 boniferous]. Barrande in his exhaustive work illustrates 

 no less than 1620 Silurian species. De Koninck in his 

 last important work upon the Carboniferous Limestone of 

 Belgium enumerates 1 70 species, amongst them many new 

 forms and many common to British strata. Prof. J. F. 

 Blake intends completing this history of the British Palaeo- 

 zoic Cephalopoda in two volumes. The part now issued, 

 being part or vol. i., treats only of Silurian species. No 

 less than 244 quarto pages and 31 plates are devoted 

 to the description of 1 1 genera and 6 sub-genera, and 143 

 species. The great genus Orthoceras being illustrated by 

 76 species, and its 4 sub-genera by 6 species, Cyrtoceras 

 23 species, Poterioccras 2, Gomphoccras 11, Phragmoceras 

 7, Ascoceras 3, Nautilus 4, its sub-genus Trochilites 3, 

 Trochoccras 12, Lituites 2, Ophidioceras 2, and Goniatites 

 (?) 2 species. These 143 species range from theTremadoc 

 Rocks, of the Cambrian series, to the Tile-stones of the 

 Upper Ludlow. Forty of the 145 species also occur in 

 Europe and America, or 32 are common to Europe and 

 6 to America, thus showing the wide distribution of 

 certain genera and species. Thirty-one plates accompany 

 the letterpress or text, every species being figured, and more 

 than 2000 specimens have been examined by the author 

 having reference to the history and description of these 

 143 species. Prof. Blake has given on pp. 233-6 a table of 

 the distribution in time of all the species, and on p. 237 a 

 condensed table showing the "growth, culmination, and 

 decay of the genera and group." These two tables are 

 suggestive, and the outcome of their study shows that 

 there were two maxima of individual abundance, one 

 occurring in the older group of rocks, the Caradoc or 

 Bala, and the other, in the Lower Ludlow, yet we feel 

 assured that there was no real diminution or falling off in 

 the variety of forms between these two deposits. The 

 tables clearly show that the species in theWenlock Lime- 

 stone were (or are now found to be) comparatively few as 

 compared with those in the shales above and below, and 

 would indicate that the Cephalopoda of the Wenlock seas 

 were not commonly frequenters of clear and shallow 

 waters, but were partly pelagic and possibly gregarious in 

 more or less turbid waters, as indicated by the impure 

 sediments composing the Ludlow shales. 



Prof. Blake has proposed a classification of the Nau- 

 Vol. xxvi. — No. 654 



tiloidea based upon the general form of the shell, and 

 having a variable siphuncle. He places all the Palaeozoic 

 forms under four groups: 1, the Coniti; 2, the Inflati ; 

 3, the Spiralesj and 4, the Irregularis. The iS genera 

 being naturally distributed through these four groups. 



Group 1. The Conici. — Receives the genus Orthoceras, 

 with its 5 sub-genera : Endoeeras, Actinoceras, 

 Tretoeeras, Couoceras, and Gonioceras, all having 

 straight conical shells ; also the curved genus 

 Cyrtoceras with its sub-genus Piloeeras. 



Group 2. The Inflati. — Receives the well-known genera 

 Poterioeeras, Gomphoeeras, Phragmoceras, Asco- 

 ceras, and Glossoceras, all possessing species with 

 curved inflated shells, and contracted apertures. 



Group 3. Spirales. — Those species with the whorls in 

 contact, of simple form and considerable curvature, 

 illustrate this group. The characteristic genera 

 are Trocholites (Silurian), Clymenia (Devonian,). 

 A/uria (Tertiary and Cretaceous), Discites (Car- 

 boniferous), and Nothoceras (Silurian), a Bohemian 

 form. 



Group 4. Irregulares. — The genera comprising this 

 group are all unsymmetrical in form, and greatly 

 curved, the genus Lituites, Trochoccras, and Ophi- 

 dioceras illustrate this division. 



Prof. Blake does not lay much stress upon the contrac- 

 tion of the aperture in the shell classification, although it 

 is important and recognised by Barrande as of much 

 significance, doubtless other features in the general struc- 

 ture of the shell weigh equally in the determination of 

 species. Such variations as are seen in rare or little 

 known forms become matters of individual opinion to the 

 species maker. As no Dibranchiate Cephalopod is 

 known, or has no representative in the Palaeozoic rocks, 

 they may be dismissed as having no place or value 

 amongst the Silurian species ; therefore the whole group, 

 whose entire history Prof. Blake has so ably described, 

 belong to the Tetrabranchiata in its two great families. 

 the Nautilidic and Orthoceratida, especially the latter. 

 Most, if not all, naturalists now agree in separating or ex- 

 cluding the Bellerophons from the Cephalopoda, although 

 Prof. McCoy, Ferrussac, D'Orbigny, Latreille, and 

 Sowerby formerly believed they belonged to the "Argo- 

 nautidae," and so placed them. 



There is still difference of opinion as to the exact limits 

 and sub-divisions of the order Orthocerata. Barrande 

 has given all the known classifications, and the characters 

 on which they have been founded by different authors. 

 They are based (1) upon the position of the siphuncle; 

 (2) the form of the suture ; (3) the involutions of the 

 shell ; (4) the form of the aperture ; (5) the symmetry or 

 asymmetry of the shell ; (6) the direction of the septa : 

 (7) the simplicity or complexity of the siphuncle. 



In Palaeozoic forms the siphuncle played a very im- 

 portant part in the life and history of the species, being 

 simple in one genus, complicated in another, dorsal in 

 one, and ventral in another, and medial in some ; the 

 genera and species have been mostly founded on these 

 changes and elements. 



The earliest group to make its appearance in time was 

 that of the Orthocerata, and out of it from the peculiarities 

 of the siphuncle and shape of transverse sections, have 

 been formed or established six genera, viz. Gonidceras, 

 Tretoeeras, Endoeeras, Aetinoceras, Bathmoceras, and 

 Bactrites, all these constitute one natural group, placed 



