9 6d YORKSHIRE TYPE AMMONITES— II Jan. 



90, 



24, 62. E. raricostatoides, Vadasz, 1908, p. 373. 



Type, E. rarecostatum ; Bayle, 1878, lxxvii, 

 2, 3. 



Cf. Am. raricostatus ; Quen, 1884, xxm, 26. 

 E. boreale, nov. T.4435D. Like Turr. boblayei, 



d'Orb., but flattened periphery, small keel, 



and fine close ribs in centre. 

 E. costidomus, Quen. 1884, xxm, 21. 



Cf. A. r. zieteni, Quen. 1884, xxm, 28. 

 E. zieteni, Quen. 1884, xxm, 27. 



Cf. Am. raricostatus ; d'Orb. 1844, liv, i, 2. 

 Ay. raricostatus ; Wright, 1878, vn, 2-4. 

 E. gracile, Quen. 1856, xm, 16. 



Cf. A. r. microdiscus, Quen. 1884, xxiv, 4. 

 E. microdiscus, Quen. 1884, xxiv, 3. 

 E. robustum, Quen. 1856, xm, 17, p. 106. 



U marinate (carina later ? Young stage of C ?) 

 E. exortum, Simpson (Y.T.A. 19). 

 E. cereum, Simpson (Y.T.A. 49). 



Cf. Am. raric. zieteni, Quen. 1884, xxm, 29. 



A. Uncarinate (cripple periphery). 

 T. in, 19, 16, 64. E. armentale, Dum. 1867, xxix, 1, 2. 



The species are arranged in order of whorl-thickness under the respective 

 headings. Owing to differences in diameters of types this does not give quite a true 

 developmental sequence among the catagenetic species ; it is, however, fairly approxi- 

 mate for them, though it may place some of the anagenetic species much out of 

 order. In each species there is development in thickness up to a maximum, and 

 then decline : the maxima fall at very different diameters in different species. 

 Renewed thickening may be expected in smooth forms. 



Information kindly permitted to be used for the above list was obtained from 

 a large series of Scotch specimens from Raasay, Isle of Mull, submitted for identifica- 

 tion by the Geol. Survey, Scotland : numbers like T.4491D. indicate these ; also 

 from specimens submitted or loaned by the Geol. Survey, England, Sedgwick 

 Museum, Cambridge, etc., as well as Radstock examples from the collections of 

 Mr. Tutcher and the Editor. 



The Raasay beds are very important. The strata yielding Echioceras are 

 about 200 ft. thick, and they give the following descending sequence : — 



Sequence of Echioceras in the Pabba Shales, Raasay. 



F. Sulcates E. cf. oosteri, E. cf. aplanatum 

 E. and subsulcates E. subquadratum 



G. Degenerates E. macdonnellii 



E. and subsulcates E. scoticum and other subsulcates 



C. Crassicostate ) E. robustum, zieteni, raricostatoides 



B. non-sulcates J E. cereum 



E. Subsulcates E. boehmi 



D.C. and non-sulcates E. laevidomus, E. edmundi 



C. Parvicostate ) E. boreale, prorsum, with Derocerates 

 non-sulcates | of the densinodum type. 



The above are some illustrative species. It will be seen that in a general 

 way the geological and biological sequences are in accord. 



