260 GILBERT C. BOURNE. 



right side. It is concealed iu a labial groove formed by two 

 deep folds of the integument, which are nothing else than 

 the greatly enlarged and modified labial palps. The extent 

 and relations of these labial folds in Anomia were first 

 described by de Lacaze Duthiers (8) and more fully by 

 Sassi (16) ; they have very much the same relations in 

 -Enigma as in that genus. The external labial fold passes 

 round in front of the mouth forming a hood and the internal 

 fold passes behind the mouth, the two enclosing between 

 them a groove of varying depth lined by a high columnar 

 ciliated epithelium, which contains numerous gland-cells in 

 the region of the mouth. On the left side of the body the 

 two folds, as they pass backward from the mouth, become 

 very deep and prominent, and enclose between them a deep 

 groove or gutter whose walls are thrown into numerous 

 vertical folds covered by a ciliated epithelium. At a short 

 distance behind the mouth the folds hang far down in the 

 mantle cavity on the left side of the foot and are suspended 

 from the visceral mass above by a thin sheet of tissue. 

 Towards the posterior end of the foot the groove becomes 

 shallower, and its walls are less folded, and eventually the 

 external labial fold unites with both the direct and the 

 reflected lamella of the left external demibranch, and the 

 internal labial fold with the direct lamella of the left internal 

 demibranch. Thus the left labial groove becomes continuous 

 with the inter-branchial chamber of the left side (see text- 

 figure 2, A and b). On the right side the two labial folds 

 run back above the byssus cavity, parallel with and below 

 the line of attachment of the right mantle lobe to the visceral 

 mass. Dorsad of the byssus the labial folds are inconspicuous, 

 the labial groove contained between them is shallow, and the 

 epithelium lining is ciliated and glandular, but not ridged. 

 Towards the posterior end of the byssus the groove turns 

 downward and backward, and the labial folds enclosing it 

 increase rapidly in vertical depth. At the same time the 

 walls of the now very deep groove are thrown into numerous 

 vertical ridges, and the epithelium of the ridges is richly 



