470 



RECENT BRACHIOPODA 



CHAP. 



other genera is the mantle of the dorsal valve, as in Cistella 

 and Argiope;^ or they may be outgrowths of the body wall in 

 the form of long processes, which are coiled and twisted in a 

 very characteristic manner in the various genera. In any case 

 the cross section of the arm shows a groove, one side of which 

 forms a continuous lip, and the other takes the form of a single 

 row of tentacles, which are richly ciliated and capable of 



Fig. 314. — View of the left half of Cistella 

 (Argiope) neapolitana, which has been cut 

 in two by a median longitudinal incision, to 

 show the disposition of the organs. Partly 

 diagrammatic. The inorganic part of the 

 shell only is shown. The tubular exten- 

 sions of the mantle and the organic outer 

 layer are not indicated, and hence the pores 

 appear open. 



1. The ventral valve. 



2. The dorsal valve. 



3. The stalk. 



4. The mouth. 



5. Lip which overhangs the mouth and 

 runs all round the tentacular arms. 



6. Tentacles. 



7. Ovary in dorsal valve. 



8. Liver diverticula. 



9. Occlusor muscle ; its double origin is 

 shown. 



10. Internal opening of left nephridium. 



11. External opening of left nephridium. 



12. Ventral adjuster. The line from 10 

 crosses the dorsal adjuster. 



13. Divaricator muscle. 



considerable movement. The whole arm in Rhynchonella can 

 be protruded from the shell, as was noted years ago by O. 

 F. Miiller, and although his statement to this effect has 

 often been doubted, its truth was confirmed by Professor 

 Morse,2 who writes : " In the 3'ear 1872, while studying liv- 

 ing Rhynchonella in the St. Lawrence, I observed a specimen 



1 Schulgin, "Argiope Kowalevskii," Zeit.f. wiss. Zool. Bd. 41, 1885. 

 ^ American Jour, of Sci. and Arts, 3rd series, vol. xvii. 1879. 



