BRACHIOPODA. 



577 



proximal part, extending almost as far as the mouth. This may be 

 called the proximal loop of the buccal groove ; its two limbs are 

 united by a mem- 

 brane. The groove 

 now turns ventral- 

 wards, and again 

 passes forwards into 

 a vertically placed 

 spiral, which is coiled 

 on to the dorsal valve 

 and at the apex of 

 which it terminates. 

 The spiral part is 

 united with the spiral 

 part of the opposite 

 side by a membrane. 

 The course of the 

 buccal groove in 



Waldhdnridis shown FlG> 460. Diagrams showing course of buccal groove in a, 



Argiope b, Waldheimia ; and c, Bhynchonella. m, mouth ; 



in the diagram (Fig. nip ; t tentacles. 

 460). The proximal 



loop of the apparatus is supported in Waldheimia and Terebratula 

 by a calcareous process of the dorsal valve (Fig. 461). In Rliyn- 



chonella there is no calcareous 

 support for the arms, but the 

 buccal groove is prolonged into a 

 long, horizontally placed spiral on 

 each side, the apex of the spiral 

 being directed to the dorsal side 

 (Figs. 460 c, 463). In Lingula the 

 arms are very much as they are 

 in Rhynchonella, the spiral being 

 horizontally placed with its apex 

 towards the dorsal valve. 



In Linc/ula and Rhynclionella it 

 appears that the animal has the 

 power of protruding its arms from 

 the shell. The epithelium of the 

 buccal groove and the tentacles is 



ciliated, and the whole apparatus is to be regarded as a food- 

 procuring organ. 



2 P 



FIG. 461. Dorsal valve of the shell of 

 Waldheimia australis, with the brachial 

 skeleton (after Hancock). 



