ANATOMY OF SCAPHULA. 



1141 



Comm. 10, 1890) and in Area americana by Ridewoocl, I. c. p. 199), 

 but interlamellar septa (present in both the above species) are 

 present, extending to about one-fourth or one-fifth the height of 

 the filament. The ciliary discs seem to be present only at the 

 free ends and at the junctions of the direct and reflected filaments. 

 They are much more numerous in all the other known genera and 

 species of the Arcidae, being arranged in many horizontal rows. 

 The arrangement of the cilia could not be followed distinctly. 

 The frontal cilia do not seem to extend much on the anterior and 

 posterior faces of the filaments. The lateral ciliary rows are 

 placed a little distance behind the frontal row. The chitinous 

 lining is uniformly thia. 



The gills of the species of ScajjJiula from Siam could not be 

 studied. Ridewood notes in species from Siam (the present 

 species?) one horizontal row of ciliary disc to the descending 

 filament and one to three such rows in the ascending one. 



Text-fiffure 3. 



Ventral view of tlie foot and visceral mass of S. celox. 



Remarks.- — The genus Scaphula Benson belongs to the family 

 Arcida3, It was recognized as such by Gray (Ann. &. Mag. Nat. 

 Hist, xix.), and by Adams and Adams (Gen. Recent Moll.). 

 Fischer (Man. Conch.) makes it a subgenus of Area., and places it 

 in the middle of his list. Dail (Trans. Wagner Free Institute of 

 Science, iii. pt. 4) makes it a group in the subgenus Barhatia. 

 Pelseneer (Lankester's Treatise on Zoology, v.) raises it to a 

 genus, and places it near the genus Area. Lamy (Journ, 

 Oonchyliol. Iv.), in his revision of the genus Area, considers it a 

 subgenus, and places it near the subgenera Area, Barhatia, Acar 

 Fossidarea, and Parallelepipedum. 



The body of the animal is characterized by an antero-posterior 

 elongation, perhaps correlated with the inequality in the size of 

 the adductor muscles. The elongation of the body has also afiected 

 the visceral mass and the foot to a relatively less extent. But 



Proc. ZooL. Soc— 1922, No. LXXVI. 76 



