H. H. Howorth—Circumpolar Lands. 305 
and is less angular, and the sinus-band is bounded by two much 
more closely set lines than in Pl. helicinoides. There is indeed a 
similar broad vertical and nearly smooth area below (anterior to) 
the sinus-band ; but, excepting this, the whole shell from the apex of 
the spire to the centre of the base is covered with regular and 
prominent rounded spiral lines; two of these spirals situated in the 
middle of the sloping posterior portion of the whorls are more raised 
than the rest, and make the whorls appear more convex; the 
periphery of the last whorl also is rounded. Very slender curved 
radial lines may be discerned throughout the shell with the aid of a 
lens; but these are fainter than in Pl. helicinoides, and almost con- 
cealed by the spirals. The base is slightly convex; a very small, if 
any umbilicus; columella indistinct, and the aperture generally very 
like that of Pl. helicinoides. Height 85 mm.; width, 7 mm. ; 
Spiral angle convex, about 75°. 
Marlstone Rock, Tilton (Hast Norton embankment). 
EXPLANATION OF PLATE IX. 
Fic. 1. Nortonia Patroclus, @ Orb., Upper Lias, Railway cutting, East Norton, 
Rutland. a. Front view; 0. back view. Enlarged twice. 
», 2. Cerithium (Cerithinella ?) confuswm, Tate, Marlstone Rock, Tilton (Kast 
Norton Embankment). Enlarged one and a half times. a, Whorl 
further magnified. 
», 98. Cerithium ferreum, Tate, Marlstone Rock, Tilton. a. Front view; 6. back 
view. Enlarged one and a half times. c¢. Whorl further magnified. 
», 4. Cerithium costulatum ? Desl., Marlstone Rock, Tilton (Kast Norton em- 
bankment). Enlarged one anda half times. @. Whorl further magnified. 
» 0. Cerithium Llminsterensis, Moore, Marlstone Rock Tilton (Kast Norton 
Embankment). «@. Front view; 6. back view. Enlarged one a halt 
times ; ¢. Whorl further magnified. 
» 6. Pseudomelania Brannoviensis, Dumort., Marlstone Rock, Tilton (Hast 
Norton embankment). Front view. Enlarged one and a half times. 
», 1. Lbid. From another specimen. Back view, similarly enlarged. 
8. Pseudomelania turbinata, Stol., Marlstone Rock, Tilton (Kast Norton Em- 
bankment). Front view. Enlarged one and a half times. 
», 9. Ibid. From another specimen. Back view, similarly enlarged. 
», 10. Turbo rugifera, Moore, Marlstone Rock, Tilton (Kast Norton Embankment. 
a, Front view; 0. back view. Enlarged twice. 
», ll. Ibid. Base, from another specimen, with an exceptionally large umbilicus. 
Similarly enlarged. 
», 12. Trochus rotulus, Stol., Marlstone Rock, Tilton (Kast Norton Embankment). 
a. Front view; 8. back view. nlarged twice. c. Whorl further en- 
larged. 
ng Be pana helicinoides, Roemer, Marlstone Rock, Tilton (East Norton 
Embankment). a. Front view; 4. back view. Enlarged four times. 
», 14. Pleurotomaria canalis, Munster, Marlstone Rock, Tilton (East Norton 
Embankment). Enlarged three times. 
(Lo be continued.) 
II].—Was THERE Aan Arctic OcEAN IN THE MammotH Periop ? 
By H. H. Howorrn, Esq., M.P., etc., etc. 
HE convergence of opinion is now so strong that the climate of 
Siberia in the Mammoth age was sufficiently temperate to 
enable trees to grow where only the bare tundra is at present found 
(if it does not necessitate our extending the forest zone at least as 
far north as the Liachof Islands), that it becomes at once interesting 
DECADE III.—VOL. VI.—NO. VII. 20 
