Vol. 52.] OF THE CHALK ROCK. 79 



Family Desmoceratidse, Zittel. 

 Genus Pachydisctts, Zittel, 1884. 



Pachydisctjs peramplus (Mantell), 1822. 



1822. Ammonites peramplus, G. Mantell, ' Foss. S. Downs,' p. 200 1822. J. 

 Sowerby, ' Min. Conch.' vol. iv. p. 79, pi. ccclvii. ; 1840. A. d'Orbigny, 'Paleont. 

 Fran?. Terr. Cret.' vol. i. p. 333, pi. c. f. 1, 2 ; 1841. F. A. Homer, ' Die Verstein. 

 des norddeutsch. Kreidegeb.' p. 87; 1842. H. B. Geinitz, ' Char, der Schichten u. 

 Petrefacten des sachsisch.-bohm. Kreidegeb.' Heft 3, p. 67, pi. xii. f. 2; 1845. A. E. 

 Eeuss, ' Die Verstein. d. bohm. Kreideformat.' p. 21 ; 1846. H. B. Geinitz, ' Grundr. 

 der Verstein.' p. 297 \{partim) ; 1846. F. v. Quenstedt, 'Petrefact. Deutschlands,' 

 vol. i. Ceph. p. 216 ; 1850. A. d'Orbigny, ' Prodr. de Paleont.' vol. ii. p. 189 ; 1850. 

 H. B. Geinitz, ' Quadersandstein. oder Kreidegeb. in Dentschland,' p. 116, pi. v. f. 1, 

 2, 3; 1852. C. G. Giebel, 'Fauna der Vorwelt,' vol. iii. p. 423; 1853. D. Sharpe, 

 ' Foss. Mollusca in the Chalk of England ' (Ceph.), p. 26, pi. x. f. 1-3 ; 1854. 

 J. Morris, ' Cat. Brit. Foss.' ed. 2, p. 298 ; 1859. A. v. Strombeck, Zeitschr. der 

 deutsch. geol. Gesellsch. vol. xi. p. 44; 1860. W. A. Ooster, 'Cat. Ceph. Foss. des 

 Alpes suisses,' part iv. p. 150 ; 1860. F. J. Pictet and G. Campiche, ' Foss. du Terr. 

 Cret. de Ste-Croix,' Pal. Suisse, pt. i. p. 354 ; 1865. ? F. Stoliczka, ' Foss. Ceph. Cret. 

 Eocks S. India,' p. 130, pi. lxv. f. 1, 2 ; 1866. C. Schhiter, Zeitschr. der deutsch. 

 geol. Gesellsch. vol. xviii. p. 71; 1870. F. Romer, 'Geol. von Oberschlesien,' p. 319, 

 pi. xxxv. f. 5; 1870. C. Schliiter, Neues Jahrb. fur Min. etc. p. 945; 1872. C. 

 Schluter, ' Ceph. ober. deutsch. Kreide,' p. 31, pi. x. f. 7-14 ; 1872. A. Fritsch and 

 U. Schlonbach, ' Ceph. der bohm. Kreideformat.' p. 38, pi. viii. f. 1-4, pi. xiv. f. 4, 5 ; 

 1874. H. B. Geinitz. ' Das Elbthalgebirge in Sachsen ' (Palaeontographica, vol. xx.), 

 part ii. p. 189, pi. xxxiv. f. 4-7 ; 1877. A. Fritsch, ' Studien im Gebiete der bohm. 

 Kreideformat. II. Die Weissenberger und Malnitzer Schichten,' p. 102; 1883. 

 Fritsch, ibid. ' III. Die Iserschichten,' p. 91 ; 1878. F. Dixon, ' Geol. Sussex,' ed. 2, 

 p. 386, pi. xxvii. f. 22 ; 1878. C. Barrois, Ann. Soc. Geol. du Nord, vol. v. p. 403. 



1840. Ammonites Prosperianus, A. d'Orbigny, 'Paleont. Franc. Terr. Cret.' vol. i. 

 p. 335, pi. c. f. 3, 4 ; 1850. F. Dixon, ' Geol. Sussex,' p. 359, pi. xxvii. f. 22 ; 1852. 

 C. G. Giebel, ' Fauna der Vorwelt,' vol. iii. p. 424. 



1840. Ammonites lewesiensis, H. B. Geinitz, 'Char, der Schichten u. Petrefacten 

 des sachs. Kreidegeb.' Heft 2, p. 39, pi. xii. f. 2 (partim). 



1842. Ammonites Decheni, H. B. Geinitz, ' Char, der Schichten u. Petrefacten des 

 sachsisch.-bohm. Kreidegeb.' Heft 3, p. 66 (partim); 1846. H. B. Geinitz, 'Grundr. 

 der Verstein.' p. 297 (partim). 



1852. ? Ammonites flaccidicostata, F. Romer, ' Die Kreidebildungen von Texas,' 

 p. 33, pi. i. f. 1 a, b. 



1865. ? Ammonites Vaju, F. Stoliczka, ' Foss. Ceph. Cret. Rocks S. India,' p. 132, 

 pi. lxv. f. 3. 



1869. (?) Ammonites f rat ernus, W. M. Gabb, Geol. Survey of California : Palaeon- 

 tology, vol. ii. p. 137, pi. xxiii. f. 15, 15 a, b. 



1873. ? Ammonites Draschei, A. Redtenbacher, ' Die Ceph. der Gosauschichten,' 

 Abhandl. d. k. k. geol. Reichsanstalt, vol. v. p. 123, pi. xxx. f. 1 a, b. 



1889. Ammonites (Pachydiscus) peramplus, A. Fritsch, ' Studien im Gebiete der 

 bohm. Kreideformat. IV. Die Teplitzer Schichten,' p. 70, f. 41 ; 1893. Fritsch, ibid. 

 ' V. Die Priesener Schichten,' p. 76. 



Description. — Shell discoidal, whorls very convex, about two- 

 thirds enclosed, siphonal area rounded. Umbilicus deep, walls 

 almost vertical. Ribs well-marked, rounded, curving forwards, and 

 continuous on the siphonal area. At the umbilical margin of each 

 whorl there are six or seven prominent sharp tubercles, each of 

 which gives rise to one, or occasionally two, primary ribs ; between 

 these there are usually three (but sometimes more or fewer) smaller 

 ribs which start from the middle of the lateral area of the whorl. 



The suture-line is figured by Sharpe (pi. x. f. 2 a) and by Geinitz 

 (1874, vol. ii. pi. xxxiv. f. 7) ; the superior-lateral lobe is trifurcate, 

 a little larger than the inferior-lateral, which is also trifurcate; 

 siphonal and lateral saddles bipartite, superior-lateral a little larger 



