232 MOLLUSCA. CEPHALOPODA. Rotalia. 



Gen. IV. ROTALIA. — The lower disc occupied by the last 

 formed whorl, the partitions of which radiate from the 

 centre to the margin ; the whorls on the upper disc ex- 

 posed. 



11. R. Beccaria. — Chambers nearly flat, numerous, the whorls 



dextral. 



N. spiralis, umbilicatus, geniculis insculptis, Walk. Test. Miu. t. iii. f. 63. 



— N. Bee. Mont. Test. Brit. 186. t. xviii. f. 4 On fuci and coral- 



lines. 



Volutions four or five, forming, above, a slightly convex disc ; the parti- 

 tions sunk, and convex on the sides ; aperture ovate, transverse near the in- 

 ner margin : the rays of the partitions of the lower disc obscure towards the 

 centre. 



12. R. Beccarii-iperyersus. — Chambers nearly flat, numerous, 



the whorls sinistral. 



N. B-p. Walk. Test. Min. t. iii. f. 6. Mont. Test. Brit. 187- t. xviii. 

 f. 6. 



This shell is found along with the last, and is said by Montagu to be 

 equally plentiful. On the Scottish coast it is greatly more abundant, and 

 grows to a superior size. 



13. R. hvflata. — Chambers tumid, few. 



Naut. inflatus, Mont. Test. Brit. Supp. 81. t. xviii. f. 3 Among sand, 



Devonshire. 



Volutions three, the last having five ventricose articulations. The upper 

 disc is more tumid, and the chambers less crowded than in either of the pre- 

 ceding species. In a single specimen found on corallines, Zetland, which I 

 possess, the whorls are sinistral, though in other respects it agrees with the 

 description of Montagu. 



Gen. V. LOBATULA. — The upper disc occupied by the last 

 formed whorl, the partitions of which radiate from the 

 centre to the margin ; the whorls on the lower disc ex- 

 posed. 



14. L. vulgaris. — Surface of the chambers frosted ; five or 

 six on the upper disc. 



N. spiralis, lobatus, anfractibus supra rotundatis subtus depressioribus, 

 Walk. Test, Min. t. iii. f. 71.— Serpula lobata, Mont. Test. Brit. 515. 

 — On shells and corallines, common. 



Upper disc convex, the partitions and centre slightly depressed, the cham- 

 bers a little rounded. Lower disc uneven, conforming to the body on which 

 it rests or adheres ; of three whorls ; aperture at the inner margin, trans- 

 verse, and nearest the lower disc. A variety, with the whorls sinistral, oc- 

 curs in nearly equal abundance. Both are subject to great variations of 

 growth. 



