90 



the very anterior besJ-s and v.ldrst about the middle of the poster- 

 ior slope. It appears to be easily discriminated from the other 

 species of this variable group knovm to the region." (Dall, 1898) 



Type locality .- Bowden, Jamaica. 



The statement, in the body of the description, that the 

 "beaks are almost posterior" involves a typographical error; the 

 beaks are anterior in position, beiiig situated at about the ant- 

 erior third of the length of the hinr^e. The posterior keel is 

 very strong and sharp and the region dorsal to it is sharply ex- 

 cavated. The sculpture is very delicate. Anterior to the post- 

 erior keel the imbricated or cancellated effect is prodiiced by 

 the superposition of strong-, somewhat irregular concentric ridges 

 on weaker, but -orominent, close-set raoiatirjg ribs of fairly const- 

 ant width, except in the extreme anterior region where they are 

 wider; dorsal to the posterior keel there are about three strong 

 radial ribs, on which the concentric ridges are but feebly devel- 

 oped, follower! by two or three narrow ribs. 



A number of detached valves of A. bowdeniana are present 

 in the collections, of these the largest is 17 mm. lon^?-, 8.5 mi}, 

 high and 4.5 mm. in semi diameter. Although there is the usual 

 variation in regularity and proportions of shaoe, certain features 

 are constant, such, as the sharpness of the posterior keel, the 

 depth of excavation of the region dorsal to the keel and the fine. 



