44 JURASSIC RHYNCHONELLIDS 
Brachial valve. There is a long, low median septum ; septalial plates are not 
developed. Inner and outer socket ridges are both present. The clearly marked 
crural bases are sharply pointed ; the radulifer crura become expanded distally. 
25 2:3 
Fic. 18. Transverse serial sections of Rhynchonella vivelensis Loriol. Oxfordian—tvans- 
versavium zone. Alex pres Oyannax (Ain), France. (8). 
