116 



BRACHIOPODA. 



(ad) ; the posterior pair near the margin, the anterior 

 near the centre of the valves and close together, especially 

 so in the ventral valve. Also other smaller muscular 

 impressions. Ordovician to present day. 



ORDER. ARTICULATA. 



The valves articulate by means of two teeth on the 

 ventral valve which fit into sockets on the dorsal. The 

 intestine is short and ends blindly. A brachial skeleton 

 may or may not be present. 



Productus (fig. 36). Shell free, generally transverse 

 (i.e. broader than long) sometimes elongated, often pro- 

 duced into ears in the umbonal region. Dorsal valve 



FIG. 36. Productus giganteus, Carboniferous Limestone. A, interior of 

 dorsal valve ; B, interior of ventral valve ; C, ideal section of both 

 valves ; D, dorsal hinge-line, j, cardinal process ; a, adductor ; 

 r, divaricator ; h, ventral area ; b, brachial prominence (?) ; s, hollows 

 occupied by the spiral arms ; v, reniform impressions. (From 

 Woodward.) 



