Yol. 52.] OF THE CHALK ROCK. 75 



1872. Helicoceras armatus, A. Fritsch and U. Schlonbach, 'Ceph. d. bohm. 

 Kreideformat.' p. 47, pi. xiii. f. 16 ?, pi. xiv. f. 14-19 (? 14, 15, 16, 18 ] ), pi. xvi. f. 9 ? 



1874. Helicoceras Meussianum, H. B. Geinitz, ' Das Elbthalgebirge in Sachsen ' 

 (Palaeontograpbica, vol. xx.), part ii. p. 193, pi. xxxv. f. 11, 12 ; 1883. ? A. Fritsch y 

 * Studien im Gebiete der bohm. Kreideformat. III. Die Iserschicbten,' p. 92 ; 1889- 

 A. Fritsch, ibid. IV. ' Die Teplitzer Scbichten,' p. 71, f. 44 ; 1893. A. Fritsch, ibid. 

 V. ' Priesener Schichten,' p. 79, f. 62. 



Description. — Shell spiral, the first few (? 5 or 6) whorls in con- 

 tact, the later ones free. Whorls circular or slightly elliptical Jin 

 section, ornamented with distant, oblique, prominent ribs (or 

 varices), each of which is produced at the same levels into four 

 short spines. Between these large ribs are smaller ones, commonly 

 four, but sometimes three, five, or six. All the ribs, particularly 

 the large ones, become less distinct on the inner (anti-siphonal) 

 margin of the whorls. 



The suture-line is much divided. Siphonal lobe of moderate size, 

 divided by a median saddle. Superior-lateral lobe larger than the 

 inferior-lateral lobe ; superior-lateral saddle a little larger than 

 the siphonal saddle, both narrow-stemmed : these lobes and saddles 

 deeply but not symmetrically bipartite, the divisions also bifid and 

 not symmetrical. Inferior-lateral saddle small, narrow, bipartite. 

 Internal lobe narrow and deep. 



Remarks. — The specimens found in the Chalk Rock consist in 

 most cases of portions of some of the later whorls only ; but one 

 example from S.W. of Dunstable in the Museum of Practical 

 Geology (No. J R 2193) shows two of the earlier whorls in contact. 

 This species has been placed by Schliiter in the genus Heteroceras, 

 but by Geinitz, Romer, and Fritsch in Helicoceras. 



Distribution. — England : Chalk Rock of Cuckhamsley, Hitchin T 

 Luton cutting, and 1| mile S.W. of Dunstable Church. France : 

 zone of Epiaster brevis at Fontaine-les-Vervins, and east of the 

 Paris basin. North-western Germany : confined to the zone of Het. 

 Meussianum, found at Salzgitter in Hanover, and Oerlinghausen in 

 the Teutoburger Wald. Saxony : Planer-Kalk of Strehlen, and 

 Weinbohla. Silesia : Scaphites-beds of Oppeln. Bohemia : Turo- 

 nian and Priesen Beds of numerous localities, e. g. Priesen, Kistra r 

 Hundoff. 



Heteroceras, sp. (PI. II. figs. 6-8.) 



Description. — Shell dextral or sinistral. Whorls elliptical in sec- 

 tion, crossed by deep oblique furrows (two or three on each whorl), 

 and ornamented with transverse, simple, oblique ribs ; on some of 

 the earlier whorls the direction of the obliquity changes, so that the 

 ribs of one whorl make with those of the next an angle of about 

 120° ; the change takes place at one of the furrows. Umbilicus 

 very wide. 



Suture-line much ramified ; siphonal lobe of moderate size, with 

 a median saddle. Superior-lateral lobe twice as large as the 



1 Figures 14, 15, and 16 are referred by Schliiter to Helicoceras reflexuTiz 

 (Quenstedt). 



