EXPLANATION OF PLATE XXXIII. 



Criockiuis JACKII, Eth. Jil. 



Fig. 1. Lateral view of the shell represented in Plate xxxii., fig. 1, an 

 imperfect internal cast ; the secondary cost;o are, in this instance, 

 almost always two between each pair of primaries. The weathered 

 sutures are quite perceptible at the distal end. 



Criockras plectoides, Eth.fd. 

 ,, 2 Portion of a septal suture. 



