Mr. J. E. Gray on the Arrangement of the Brachiopoda. 439 



Fam. 3. Discintd^e. 



The upper valve is conical and patelloid, the lower orbicular, 

 and is attached to marine bodies by a short tendinous peduncle, 

 which passes out through a slit in the hinder part of the disc of 

 the ventral valve. 



The animal of this genus has been described by Mr. Owen 

 under the name of Orbicula, Mr. G. B. Sowerby having some 

 years ago confounded this shell with that genus, which has 

 caused confusion which has existed to this day. The shell was 

 first described by Schumacher as a section of the genus Crania : 

 Mr. King, probably misled by this mistake, does not include it 

 in his arrangement. This shell is peculiar, for being a horny 

 rather than a shell texture, it is flexible when moist. 



Fam. 4. Lingulid^e. 



The valves are nearly equal, elongate, and supported by a thick 

 peduncle which comes out between the beaks of the two valves. 

 The shells are covered with a horny periostraca, and in some spe- 

 cies the shelly matter is so very thin that the shells are flexible 

 and nearly entirely cartilaginous. 



The family contains only a single genus, Lingula. 



Order V. Rudistes. 



This order has been placed by most modern authors with the 

 Brachiopoda : the proofs of its belonging to this family are not 

 very evident ; but as there is no other to which they appear to be 

 more nearly allied, they may as well be retained in this position. 



Lamarck, Cuvier, Ferussac, and some other authors have re- 

 garded some of the genera as belonging to Cephalopoda, and 

 others as bivalves (Conchifera). 



Deshayes regards them as more nearly related to Chama, the 

 character of the family having been lost by the destruction of 

 the inner coat of the shell during the fossilization of the speci- 

 men. 



M. D'Orbigny has properly united them into one group under 

 the name of Irregular Brachiopods or Rudistes, but he includes 

 with them the genus Crania, which is a true Brachiopod. 



They form three very distinct families : — 



Fam. 1. RadiolitidjE. 



The lower valves more or less elongate-conical, fixed ; the up- 

 per valve conical or spiral, free ; the texture of the lower valve 

 cellular or fibrous. 



The Radiolites has the upper valve flat or conical and cap-like. 



The Caprina, D'Orb., has a spiral and produced upper valve. 

 The first of these genera has had many names applied to it, but 



