190 



BRITISH PALAEOZOIC ASTEROZOA. 



plate (" la dent'') ; the one, a wedge, which projects into the interior of the mouth 

 ("la dent proprement dite ") ; the other ("la branche montante "), a limb which 

 projects upwards to unite with the first ambulacral. On this ascending limb is 

 a wing-shaped apophysis which has two faces separated by a swollen ridge carrying 

 important muscles, which will be described later. The first ambulacral is thickened 

 on its proximal surface, and the thickened portion meets the ascending limb. The 

 distal half of the ambulacral sends down a slender pillar on to the body of the 

 mouth-angle plate. Between the pillar and the ascending limb is a long slit for 

 the passage of the ampulla of the first tube-foot. Ludwig, contemporaneously 



Text-fig. 132. — Arrangement of the ossicles of the groove and mouth-region of a very young Asteroid 

 (after Ludwig). Ad. x , first adambulacral; Ad. v second adambulacral ; Am. x , first ambulacral; Am.,, 

 second ambulacral ; Am. 3 , third ambulacral ; F. u opening for ampulla of first tube-foot : F.», opening for 

 ampulla of second tube-foot ; M.P., mouth-angle plate ; 0., odontophor ; T., terminal, x 170. 



with Viguier, published a description of the mouth-frame which, on account of the 

 reputation of the author, has achieved wide publicity. He regarded the ascending 

 limb with the thickened portion of the first ambulacral— -that is, the calcite bar in 

 front of the first ampullal pore — as a separate ossicle, " the real first ambulacral." 

 This allowed him to consider the mouth-angle plates as being the adambulacralia 

 corresponding to his real first ambulacral, otherwise it was necessary to regard the 

 mouth-angle plates as plates distinct from any other in the ambulacral groove. 

 Thus, according to Ludwig, the mouth-frame was merely the modified proximal 

 portion of the ossicles of the grooves. All later workers have omitted to notice 

 that Ludwig himself withdrew this interpretation. So long ago as 1897 Ludwig 



