190 



GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



Description. Exterior. — Subpentameral in out- 

 line; hinge-line narrow; lateral profile subequallv 

 biconvex; anterior commissure uniplicate, the fold and 

 sulcus being defined at the front half. Ventral beak 

 curved over the dorsal. Surface smooth ; test fibrous, 

 impunctate. 



Ventral interior. — In the ventral valve there is a 

 long spondylium supported for nearly its full length 

 by a high median duplex septum which extends for 

 nearly half the length of the valve. 



Dorsal interior. — There is a small and short cru- 

 ralium supported by a high septum. This cruralium is 

 partially covered by lateral plates which overhang the 

 notothyrial margins much as deltidial plates, repre- 

 senting a divided hinge-plate. In a valve about 



20 mm. long the subrostral chamber is only 2 mm. 

 in length. 



Geologic range. — Silurian of Bohemia. 



Discussion. — At first it appears difficult to assign 

 Lioccelia to its proper place among either the pentam- 

 erids or the rhynchonellids. The external form is 

 essentially pentameroid, and the ventral valve with its 

 spondylium duplex is a normal pentameroid feature. 

 But in the dorsal valve the cardinalia are rather those 

 of the rhynchonellids, such as Camerofhoria, especially 

 in the small subrostral vault. It would thus appear 

 that Liocaelia is essentially a smooth Camerofhoria 

 having an external form like that of Clorinda, Merista, 

 or Meristella. 



