338 



POPULAR CONCHOLOGY. 



Family 2. — RHYNCH ONELLID^E. 



The mouth arms are prolonged, fleshy, supported at the 

 base by two short, diverging laminae, which spring from 

 the hinge of the ventral valve. The shell is not perforated, 

 usually radiated ; the hole for the passage of the tendon 

 is not in the point of the boss itself, but below it, there- 

 fore the boss remains pointed. 



Rhynchonella. Fischer. (Cyclothyris and Semi- 

 luna M'Coy; Lampas Gray; Hypothyris Phillips.) — 

 Shell free, fibrous (not of perforated structure), oval or 

 transverse, depressed or gibbose, inequivalve, upper valve 

 larger, without a distinct area, with a produced, incurved 

 beak ; lower valve gibbose, with its apex concealed in the 

 upper valve ; opening small, round, below the point of the 

 beak of the larger valve, surrounded by a tubular pro- 

 jection, and separated from the lower valve by a deltidium 

 formed of two pieces soldered together ; the inner scaffold 

 is attached to the under valve on each side of a long 

 apophysis, which is flat, and almost channel-formed, spring- 

 ing from the hinge and ending in a broad part which bears 

 the free fleshy arms. — 1 species ; also fossil. 



The only living species is the Terebratula psittacea of 

 the Northern Icy Seas. The fossil species found in the 

 chalk formations are T. percgrina of Buch, depressa, Sow., 

 lata, Sow., and vespertilio, Broc. 



Hemithyris. D'Orb. — Shell free, fibrous, oval or 

 transverse, gibbose, inequivalve ; the upper valve larger, 

 convex, without distinct area, with a produced incurved 

 beak ; lower valve gibbose with its apex concealed ; open- 

 ing in the upper valve, small, oblong, in the form of a slit, 

 reaching from the edge of the lower valve to the beak, 

 without any deltidium. — Fossil. 



