874 MANUAL OF THE MOLLUSCA. 
Sub-genus? Merista, Suess. Ter. scalprum, Roemer. (A. 
cassidea, Quenst. Sp. plebeia, Ph.) Silurian 
—Deyonian. Europe. Shell impunctate, 
dental plates (v) and dorsal septum (d) sup- 
ported by arched plates (‘‘ shoe-lifter”’ 
processes, of King) which readily detach, 
leaving cavities (as in Fig. 171); spiral arms 
Fig, 171. Merista. Shaye been observed in all the species. 
RETzIA, King. 
Dedicated to the distinguished Swedish naturalist, Retzius. 
Type, Ter. Adrieni, Vern. 
Example, R. serpentina, Carb. L., Belgium, Fig. 172. 
Shell punctate, terebratula-shaped; beak truncated by a 
round foramen, rendered complete by a distinct deltidium ; 
hinge-area small, triangular, sharply defined; interior with 
diverging shelly spires. 
Fossil, about 50 species. Silurian—Trias. South America, 
United States, Europe. 
Professor King first pointed out the existence of calcareous 
spires in several Terebratulce of the older rocks, and others have 
been discovered by MM. Quenstedt, De Koninck, and Barrande. 
In form they resemble Terebratulina, Hudesia, and Lyra. 
Fig. 172. Retza serpentina, D. K. Fig. 173. Uncites gryphus. 
UncitTEs, Defrance. 
Type, U. gryphus, Pl. XV., Fig. 17. Fig. 173. 
Fossil, Deyonian. Europe. 
Shell impunctate; oval, bi-conyex, with a long incuryed 
beak; foramen apical, closed at an early age; deltidium large, 
concaye; spiral processes directed outwards; no hinge-area, 
The large, concaye deltidium of Uncites so much resembles 
the channel formed by the dentai plates of Pentamerus, that 
