WORMS. U>i 



38. TELLIXA. Inhabitant a Tethya : shell generally slop- 

 ing and somewhat curved on one side : hinge with 

 generally 3 teeth, the lateral-ones in one valve flat or 

 nearly obsolete. 



39. CARDIUM. Inhabitant a Tethys : shell of equal con- 

 vex valves, ribbed or striate longitudinally, toothed 

 round the edges . hinge with 2 teeth near the beak, 

 and a larger remote one oil each side, each locking 

 into the opposite valve. 



40. MACTRA. Inhabitant a Tethys: shell with equal 

 valves, unequal at the sides : hinge with the middle 

 tooth complicated, with a small hollow each side; 

 the lateral-teeth remote and locking into the oppo- 

 site valve: 



41. DONAX. Inhabitant a Tethys : shell with the ante- 

 rior margin very obtuse and generally crenulate : hinge 

 with 2 teeth in the middle, and a single remote late- 

 ral one. 



42. VENUS. Inhabitant a Tethys j shell with the anteri- 

 or margin of the lip of one valve generally incumbent 

 on the other : hinge with 3 teeth, all Close together, 

 the lateral-ones diverging from their tips. 



43. CHAM A; Inhabitant a Tethys : shell strong, rather 

 coarse ; hinge rugged, gibbous, the teeth obliquely 

 locking into the opposite valve. 



44. ARCA. Inhabitant a Tethys: shell of equal valves : 

 hinge with numerous sharp teeth alternately locking 

 between each other. 



45. PECTEN. Inhabitant a Tethys: shell of unequal 

 valves, mostly ribbed or striate longitudinally, with 

 an ear-like process on one or both sides the hinge : 

 hinge without teeth, but furnished with a small some- 

 what triangular hollow. 



46. OSTREA. Inhabitant a Tethys: shell of unequal 

 rugged or plaited valves without the ear-like pro- 

 cess : hinge without teeth, with a transverse striate 

 cavity. 



47. ANOMIA. Inhabitant not reducible to any genus of 

 Mollusca: shell of unequal valves, one of them 

 flattish and mostly perforated near the base, the 

 other convex at the base with a produced beak : 

 hinge a transverse linear prominence on the flat valve 

 connected by a strong cartilage under the beak of tlio 

 opposite valve. 



48. MYTILUS. Inhabitant allied to an Ascidia : shell 

 generally affixed by a beard of silky filaments : kings 

 without teeth, marked by a longitudinal groove 

 which is sometimes crenulate. 



49. PINNA. Inhabitant allied to an Ascidia: 



