Bitlla. 
MOLLUSCA. BRANCHIFERA. 
EXTINCT SPECIES. 
1. B. convoluta — Cylindrical, smooth ; aperture linear, expanded a little 
way from the base ; vertex obtuse, perforated. — Sower. Min. Conch, t. 
cccclxiv. f. 1. — In Crag. 
2. B. cmstricta. — Subcylindrical, contracted in the middle ; vertex trun- 
cated, perforated ; base obscurely striated ; aperture linear, expanded at the 
base. — Sower. Min. Conch, t. cccclxiv. f. 2. — London clay.^ Barton. 
3. B. elUptica — Elliptical, elongated, transversely striated ; vertex perfo- 
rated ; aperture widest at the base. — Sower. Min. Conch, t. cccclxiv. f. 6 
London day., Barton. 
4. B. attenuata. — Elliptical, transversely striated; superior portion elon- 
gated, truncated, perforated ; aperture curved, widest towards the base ; striae 
distant in the middle — Sower. Min. Conch, t. cccclxiv. f. 1i.~^London clay. 
Hordwell. 
5. B.^fosa.— A fragment. “ Its numerous striae and expanded lip distin- 
guish it from B. attenuata.”— Min. Conch, t. cccclxiv. f. 4. 
