( 471 ) 



direction; just undcrnefitli the liook tlie riilge is bigliest; the nnmbcr of teeth is 

 variable. 



The variation according to locality affects especially the length of the longi- 

 tudinal (ventral) and the ventri-dorsal ridges, their outline and armature, and the 

 height of the oblique fold. 



a. I', cuchenof euchenor: f. 51 to 54, 59 to 61. 



The variation noticed by us in the ventral ridge of New Guinea individuals is 

 represented in views from the dorsal side in f. 52 to 54. The usual form of the 

 ridge is given in f. 62, taken from an example from Constantinhafen, .German 

 New Guinea (f. 51 is taken from the same individual). In f. 53, representing a 

 specimen from the same localitj-, the ridge is very high in the basal third and then 

 rather suddenly diminishes in height ; and iu f. 54, taken from a specimen from 

 Simbang, near Finschhafon, Huon Golfe, the iibrujitly raised liasal portion is rather 

 angnlate. 



Our sjiecimens from the D'Entrecasteaus group of islands, east of New Guinea, 

 as well as those from Waigen, west of New Guinea, come iu respect to the ventral 

 ridge within the limits of variation as illustrated by f. 52, 53, 54. All tlie 

 specimens have the angle formed by tlie sudden break iu the outline of the ridge 

 jiroduced into the beak-like basal hook. 



The vertical (ventri-dorsal) ridge is Tepresented separate from the ventral ridge 

 in order to be able to give the exact outline ; f. 59, 60, 61, are taken from the 

 same individuals as f. 52, 53, ^4 respectively. As f. 59 to 61 are drawn from 

 a basal view of the ridge, the veutri-apical hook (/>) has a difierent appearance from 

 that iu f. .52 to 54. 



The higher dorsal (left-hand side in figure) portion of the ridge is dentate; 

 just at the highest point, or close to it, stands nearly always a stronger tooth, which 

 in f. 59, however, is obsolete. The sj)ecimens from the D'Entrecasteaux Islands 

 have nearly all the ridge toothed similarly to f. 61, a character which becomes 

 more obvious in the individuals from WooiUark Island. The interesting aberration 

 from Jobi Island, P. euclienor euchenor ab. eutropin/i, does notpresent any peculiarity 

 in the valval armature. 



b. P. encltenor gotlarti ; f. 58. 



We have examined three specimens of this form, which is all known to exist in 

 ccdlections, except Montrouzier's tj^pe-specimen which is perhaps (? !) preserved iu the 

 Paris Musevmi. Tlie only distinguishing character in the valve and its armature 

 found in all tliree individuals concerns tlie oblique fold ('/), which is higher than in 

 either euchenor obsolescens or euchenor euchenor; the valval cavity before and behind 

 the fold is consequently deeper. The ventral and ventri-dorsal ridges are not con- 

 stantly different from those of the New Guinea individuals ; the dentition of the 

 vertical fold is, however, in all three examples rather plentiful. The more aberrant 

 harpe of the three is represented by f. 58 and 64 ; the ventral ridge (f. 58) is 

 distinguisliol by the long basal and relatively short veutri-apical hook, and by the 

 upper edge of the ridge being feebly and widely bisinuate ; the ventri-dorsal ridge 

 is multidentate. 



c. 1'. euchenor obsolescens; f. 55, 56, 57, and 62, 63, 64. 



In Aru individuals the ventral (longitudinal) ridge is somewhat shorter than in 

 euchenor euchenor, and the vertical ridge accordingly longer, as will be seen by 



