Photo File:The Quarterly journal of the Geological Society of London (

bhl | titre the quarterly journal of the geological society of london. | source https://www.flickr.com/photos/biodivlibrary/12960575004 | description j. w. datis ox the gextj8 pleur acanthus, agass. 335 surfaces are round and smooth ; the posterior is depressed, one tenth of an inch across at the base, contracting to a small groove towards the apex ; the angles formed by the contact of the posterior and fig. 10. ? pleuracantlius denticidatus ^ davis. denticles of the spine, enlarged. lateral faces are armed with a series of closely set denticles (fig. 10), which are small, comparatively broad at base, contracting suddenly, then forming a carinated apex, pointed at the extremity towards the base of the spine. there are 20 denticles on each side in the space of an inch ; and in the specimen figured there are 45 on each side. a circular cavity (which appears, as usual, to be terminal) ex- tends towards the point ; it is large in diameter in proportion to the spine. locality. better-bed coal, clifton, near halifax. several specimens which have been obtained from the cannel coal at tingley may probably be referred to this genus. they pre- sent some points of difference ; but these may probably be accounted for by the relative position of the two stratigraphically, the cannel coal being several hundred feet higher in the coal-measure series than the bone-bed. the tingley spines are slightly compressed laterally ; the anterior and lateral faces are striated near the basal extremity ; the posterior denticles are small and much resemble those of the bone-bed specimens ; the base is better exposed, its walls are rather thin, and the internal cavity is large ; the spines ex- pand towards the base. a perfect example will be about 3*5 inches in length. p. denticidatus appears to be most nearly associated with p. wardi, and with a spine described by dr. newberry (in the palae- ontological volume of the ' survey of ohio,' vol. i. p. 332, pi. lix. fig. 4) as ortliacanilius arcuatus. the latter is described as finely striated longitudinally on the anterior surface ? the posterior surface occupying one third the circumference, and having a low ridge along the median line. the denticles extending along the latero-posterior angles are much closer together and more numerous, and from the figure appear to be quite different in character from those in my spe- cimen. in all these particulars the two species arc clearly divergent ; in other respects they are similar ; in curvature and general form they are evidently very closely related. p. denticidatus is easily distinguished from p. wardi by the largo size of the latter, the pecuhar squareness of its lateral faces, and its obtuse teeth connected together by intermediate ridges. in these respects they differ essentially from each other. | pageid 36090694 | itemid 111264 | titre id 51125 | pagenumbers page 335 | pagetypes text | volume 36 | pageurl https://www.biodiversitylibrary.org/page/36090694 | date 1880 | auteur geological society of london | names namefound:ortliacanilius arcuatus namefound:p. denticidatus namefound:pleuracantlius denticidatus | permissions biodiversity heritage library | | other_fields information field | nameflickr sets | valueflatlist | *the quarterly journal of the geological society of london. v. 36 (1880). information field | nameflickr tags | valueflatlist | *geology *periodicals *smithsonian libraries *bhl:page 36090694 *dc:identifier https://www.b

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