198 



tinct orbicular disk on each ; the disk of the upper valve 

 submammillated and undivided, the mammillae surrounded 

 by fine radiating striae ; the other valve very white, and 

 divided by a transverse slit: there is no trace of hinge' 

 ligament, or impression. Recent. 



7. Crania. An unequal valved, soborbicular bivalve ; 

 the under valve flat, fixed beneath, the inner surface 

 pierced with three unequal and oblique foramina ; the upper 

 valve is convex, subgibbous, with two prominent callosities 

 at its base. Fossil. The under valve. PI. vii. fig. 21. 



JSrachiopodes, conchifera. Having, near their mouths, 

 two opposite elongated ciliated arms rolled in spirals when 

 at rest. Mantle, with two lobes separated forwards, wrap- 

 ping up or covering the body. A bivalve shell adherent to 

 marine bodies either immediately or by a tendinous cord. 



The genera of this family are Orbicula, Terebratu/a, 

 and Lingula. 



1. Orbicula. A suborbicular, unequal valved bivalve, 

 with no perceivable hinge ; the lower valve is very thin, flat, 

 and affixed beneath ; the upper valve is subconical, with a 

 pointed top, more or less prominent. 



This shell is described, by Muller, Zool. Dan. i. p. 14, 

 Tab. v. fig. 17; and, by Poli, Conch. Vol. ii. p. 189, 

 Tab. xxx. fig. 15. 



A fossil shell of this description is found in the iron 

 stone nodules in Shropshire and Worcestershire. 



2. Terebratula. An inequivalved, regular, subtrigonal 

 bivalve, attached to other bodies by a short tendinous 

 pedicle ; the largest valve has an advanced beak generally 

 incurved, and pierced either by a round hole or a notch, 

 through which its organ of attachment passes ; the hinge 

 with two teeth. In the inner part are two subosseous, thin, 

 forked, and variously ramified branches, proceeding from 

 the disk of the small valve, and supporting the animal. 

 Recent and fossil. PI. vii. fig. 23. 



