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| Keywords: The Quarterly journal of the Geological Society of London (12960135525).jpg 330 J W DAYIS ON THE GENUS PLEURACANTHUS AGASS <br> 8 Pleueacanthtjs eobijstus sp nov PL XII fig 5 <br> Spine Length 3 5 to 4 5 inches Breadth about mid-length -4 <br> of an inch JFrom the middle the diameter of the spine becomes <br> smaller in each direction ; towards the apical extremity it contracts <br> rapidly and terminates in an obtuse point ; the base is reduced to <br> three fourths the largest diameter The spine is straight along the <br> dorsal side ; the opposite one slightly curved The lateral and an- <br> terior surfaces are covered with fine but very decided longitudinal <br> furrows numerous towards the base and disappearing without <br> anastomosis towards the apex The general form of the spine in <br> section fig 7 a h is rotund the lateral faces being produced out- <br> wardly so as to meet the more depressed curvature of the dorsal <br> aspect The dorsal surface is wide embracing nearly one third of <br> the entire circumference of the spine It is produced so as to form <br> a large median ridge ; and along the centre of this there are a number <br> Fig 7 ” Pleuracantlius rohustus Davis <br> a b <br> Si <br> a Section of the spine near the base h Section nearer the point <br> c Denticles enlarged <br> of small punctures which occasionally coalesce and form a slight <br> groove On each side of the median ridge is a proportionally deep <br> furrow The angles formed by the outer edges of these furrows <br> and the sides of the spine are armed with a series of large closely-set <br> acuminate denticles fig 7 c They extend from the surface of the <br> spine ˘ of an inch being nearly one half the diameter of the spine <br> they are very strongly implanted and recurved towards the base <br> The outer surface of the denticle i e the one forming the largest <br> curve is produced in the form of a minute carina or keel There <br> are about twenty denticles extending rather less than one half the <br> length of the posterior face The internal cavity is round and <br> except at the base is comparatively small ; it is in the centre of the <br> spine The walls of the cavity are thin where it has been imbedded <br> in the muscles of the flesh ; they gradually gain in thickness and <br> strength until the cavity ends in a point about 1 inch from the distal <br> end the remaining part being solid <br> The preceding species viz PleuracantJius robustus alatus and <br> altemidentatus possess features in which speaking broadly they are <br> somewhat similar to each other Whilst however they possess this- 36090689 111264 51125 Page 330 Text 36 http //www biodiversitylibrary org/page/36090689 1880 Geological Society of London NameFound Pleueacanthtjs eobijstus sp NameFound Pleuracanthus NameConfirmed Pleuracanthus EOLID 20530464 NameBankID 2879732 NameFound Pleuracantlius rohustus Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 36 1880 Geology Periodicals Smithsonian Libraries bhl page 36090689 dc identifier http //biodiversitylibrary org/page/36090689 smithsonian libraries Information field Flickr posted date ISOdate 2014-03-06 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/12960135525 2015-08-26 15 53 24 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1880 Photos uploaded from Flickr by Fæ using a script | ||||
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