NEWTON AND HAKKIS : OLIGOCENE AND EOCENE PULMONATA. 77 



Planoebis euomphalxjs, J. Sowerby. PI. VI. Pigs. 10-11. 



Planorhis euomphalus, J. Sowerby. — Mineral Concliology, 1816, 

 vol. ii. p. 92, pi. cxl. fig. 7. P. E. Edwards. — Mon, Pal. Soc. 1852, 

 p. 99, pi. XV. fig. 6. 



Planorhis (Jleh'soma) euomphalus. — Cossmann, Ann. Soc. R. Mai. 

 Belgique, 1889, vol. xxiv. p. 334, pi. ii. figs. 41-42. 



Two specimens belonging to this species have been selected for 

 illustration and remark on account of their eccentric shapes. One 

 (Pig. 11) displays a curious distortion which has taken place on the 

 inferior or umbilical surface of the test (regarding this as clextral), 

 giving the apjjearance of a double kind of growth or twinning. 

 Prom an examination of the aperture this is clearly one shell, as 

 beyond a sharp depression in the outer lip there is no indication of 

 a diaphragm of any kind. Notwithstanding this resemblance to a 

 secondary growth the depth of the entire shell corresponds with that 

 of the species under ordinary circumstances ; in fact, in all other 

 respects it does not depart from the normal form. 



The next specimen (Pig. 10) represents the outer whorl disengaged 

 from the earlier volutions, and continuing a spiral course with the 

 aperture directed upwards. The basal view exhibits the younger 

 portion of the spiral system intact, and forming the umbilical cavity. 

 There is a line of weakness on the fifth whorl, possibly a fracture 

 sustained during the life of the mollusc, which would probably account 

 for this unusual departure in its growth. 



Formation. — Oligocene (Headon Beds). Locality/. — Headon Hill. 



EXPLANATION OF PLATE VI. 



Fig. 1. — Entaliopsis annulata. n.sp. 

 ,, 2. — Limnasa Headonensis, n.sp. 

 ,, 3. — Megaspira monodonta, n.sp. 

 ,, 4. — Cochlicopa Headonensis, n.sp. 

 ,, 5. — Isthmia diibia, n.sp. 

 ,, 6. — Pupa multispirata, n.sp. 

 „ 7-9.— Pitliarella Rickmani, F. E. Edwards. 



,, 10, IL — Planorbis euomphalus, J. Sowerby (monstrosities). 



,, 12. — ,, incertus, n.sp. 



,, 13. — Vitrea Sconciensis, n.sp. 



,, 14. — ■ ,, leia, n.sp. 



,, 15. — Helix pseudo-globosa ? Oih. \_Juv.']. 



