12 



BRITISH PALEOZOIC ASTEROZOA. 



ventral side of the ray, near its tip, perhaps the ray bends downward and under at 

 precisely the point where the food body touches it, so as to bring the food into 

 contact with a point on the lower surface of the ray nearer the disc. The tube- 

 feet of this nearer point then seize the flesh, while the more distal ones release it. 

 Now the point at present bearing the food bends downward, applying it to a new 

 region, whilst the point first bent straightens out. Thus the food is passed from 

 one set of tube-feet to another, slowly along the under side of the ray, till it 



A-iA-.A A^Pi 



,^',M. A. P. 



PROXIMAL. 



d.JI.(6) R. 



Am. Ch. 



Am. p. 



DISTAL. 



S. 31. 



M{2) 



Am. 1). 



M.(3) 



Text-fig. 3 (on left).— A fifth part of the skeleton of Pentacevos reticulatus, oral view (after A. Agassiz). 

 M. A. P., mouth-angle plates ; A^, first ambulacral ; 4iPi, anterior process of first anibulacral ; A.2, second 

 ambulacral ; Ad., adambiilacralia ; V. L., ventro-lateralia ; S. M., supero-marginalia ; /. M., infero-marginalia ; 

 Ami. Gr., ambulacral groove; Atn.p., ambulacral pore. 



Text-fig. 4 (above). — An oral view of two pairs of ambulacralia and adambulacralia of Archader typicxis. 

 Am. Ch., ambulacral channel; B., ambulacral ridge; d. M.(6), points of attachment of the ventral trans- 

 verse muscles; Am. p., ambulacral pore for the passage of tube leading to the ampulla. 



Text-fig. 5 (below). — A disarticulated ambulacral and adambulacral oi Archasler typiicus. 1, facet on apophysis ; 

 2, facet on wing ; remaining abbreviations as in previous text-figures. 



reaches the mouth." This process is probably a survival of the earliest manner 

 of feeding, 



(ii) The Arm as seen in Oral {Ventral) Vieiv. — Text-fig. 3 gives a good typical 

 oral view of an Asteroid. The specimen after death dried in such a manner that 

 the ambulacral groove has opened out, giving a clear view of the ambulacral 

 ossicles. Much more frequently the groove closes after death, and the adambu- 



