442 DISCOVERY REPORTS 



of records must have been established. We regard them merely as the local types of one 

 species of almost world-wide distribution. Between these two extremes almost every 

 conceivable variation can be found, and no scientific purpose appears to be served by 

 the multiplication and resuscitation of useless specific names. 



The Falkland specimens present considerable variation in the thickness of the shell. 

 D'Orbigny separated his species from P. lessonii "par son centre ombilical convexe au 

 lieu d'etre concave", but, as a matter of fact, the Falkland specimens show great range 

 of variation. In some the umbilicus is highly convex and clear, and except for the smaller 

 size of the specimens, are of the Mediterranean type; in the others the shell is almost 

 flattened on both sides, and at WS 86 the flattening goes to the extent of a depressed 

 umbilicus. Between these extremes every possible variation is to be found. 



The Paris Type tube contained five specimens; one of them is entirely destroyed by 

 efflorescence, and one is P. alvareziana, a very good specimen from which the figure of 

 that species might have been drawn. Of the other three, one is identical with d'Orbigny's 

 figure, the other two represent transitional stages towards the formation of the central 

 umbo which distinguishes P. crispa. 



