184 



Terebratula rubra. PI. P. Pig. 2. Shell, with the valves opened to 

 show the internal apophysary skeleton. 



Genus 2. RYNCHONELLA, Fischer. 



Animal ; with spirally coiled arms, not fixed by any looped carti- 

 laginous apophysis, but supported at the base ojily by two short 

 curved processes. 



Shell ; inequivalve, equilateral, subylobose, grooved or striated, 

 never punctured ; upper valve sharply beaked over the lower ; 

 beak entire, triangularly perforated beloio ; no deltidium ; lovjer 

 valve furnished at the hinge-margin on either side with a 'pro- 

 jecting curved blade. 



Rhgnchonetta, of which the well-known R. psittacea, or Parrot's-beak 

 Terebratula, is the type, differs essentially from the preceding genus. The 

 animal has no cartilaginous apophysis for the support of its cirrhated arms. 

 A hooked blade projecting from the hinge-margin of the lower valve on 

 either side supports each arm at its origin, and beyond this they are dis- 

 posed in six or seven free spiral gyrations which are unfolded and pro- 

 truded outwards, and again retracted at pleasure. The position of the 

 animal is the same as in Terebratula, but the foramen in the upper valve, 

 for the passage of the tendinous pedicle, is not at the extremity of the 

 beak, but under it, the beak being sharply over-hooked. The shell, more- 

 over, is not punctured, and it is a feature in the geological history of 

 Rhynclionella that as many as two hundred and eighty species are known 

 in a fossil state, while only two are found living, one a native of the north- 

 ern Atlantic seas, the other of the seas of New Zealand. 



Species. 

 1. nigricans, Sow. 2. psittacea, CJiemn. 



Figure. 



Rhynchonella psittacea. PL P. Pig. 3. Shell, placed on end to show 

 the foramen beneath the hooked beak. 



