THE BRITISH FOSSIL BRACHIOPODA. 



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families and genera in which they were folded back upon themselves and supported by a 

 calcareous skeleton as in Waldheimia. 



Fig. A. 



Fig. B. 



Waldheimia Jlavescens. 



Fig. A. Interior of dorsal valve to show the position of the lahial appendages (a portion of the 

 fringe of the cirri has been removed to show the brachial membrane and a portion of the spiral extre- 

 mities of the arms). Enlarged. 



Fig. B. Longitudinal section, with a portion of the animal, d, h, brachial appendages; a, adductor; 

 c, c', divaricator muscles; s, septum; v, mouth; z, extremity of alimentary tube. The peduncular 

 muscles have been purposely omitted. Enlarged. 



In Rhynchonella t where the elongated spiral appendages are supported only at their 

 origin by two short, curved, projecting calcareous processes, they could be unrolled 

 at the will of the animal and protruded to some distance beyond the margins of the 

 valves. When forcibly stretched out, they are said to be more than four times the length 

 of the shell, and support some 3000 cirri. See Hancock's admirable illustration of the 

 animal of Rh. psittacea, reproduced here in PI. XXI, fig. 3. 



In a note on the extension of the coiled arms in Brachiopoda, Professor Morse says : 

 " Years ago von Buch recorded that Otto F. Miiller had observed Rhynchonella 

 psittacea protrude its arms beyond the anterior borders of the shell. This single 

 observation was not widely accepted, and many doubted the possibility of the arms being 

 exserted in this manner. In the year 1872, while studying living Rhynchonella in the St. 

 Lawrence, I observed a specimen protrude its arms to a distance of four centimetres 

 beyond the anterior borders of the shell, a distance nearly equalling twice the length of 

 the shell. This year I again had an opportunity of studying Rhynchonella in Hakodate, 

 Yesso, and again observed the same features. Specimens lying on the bottom of a glass 

 dish protruded their arms a short distance and remained in this position for hours. The 

 movements of the arms were very sluggish, though the cirri were constantly in motion. 

 Sometimes the shells closed upon the arms before they were retracted. Lingula has the 



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