bartsch:' subspecies of obba marginata 61 



ing the light peripheral zone and another situated at about one-third 

 of the distance between the periphery and the unibihcus anterior to 

 the periphery. Here, as in the banding of the upper surface, we find 

 a considerable variation both as to intensity of coloration and width of 

 the band. In some the zone at the periphery is merely indicated 

 (Obba marginata lanaona and Obha marginata mearnsi), while in others 

 they are very dark and broad (Obba marginata marginata and Obba 

 marginata balutensis). In all the forms the basal lip is toothless. 

 Under the microscope we find that the first half turn is smooth; the 

 turn and a half followi.ig this are marked by slender oblique, retrac- 

 tively curved, axial threads, best seen near the summit and at the 

 periphery; while the succeeding turns have in addition to these threads, 

 very fine, closely spaced, impressed lines which cross each other more 

 or less" at right angles and the lines of growth at an angle of about 45° 

 and give the surface a fine cloth-like texture. 



The various subspecies of Obba marginata can readily be divided into 

 two groups, one in which the dark coloration predominates over the 

 light zones and another in which the reverse is true. To the first of 

 these, the dark group, belong the subspecies saranganica, balutensis, 

 marginata, ivorcesteri, and boholensis. In the light group we find 

 characters that readily enable one to further subdivide it. In two 

 forms (mearnsi and palmasensis) the shell is broadly conic. In the 

 rest the shell is lenticular. This last complex is again divisible. One 

 part (subspecies griseola, samarensis, pallescens, and nana) has the 

 basal peripheral band well developed. In the other (subspecies zam- 

 boanga, lanaona, and joloensis) the basal peripheral band is obsoletQ. 



The distribution, as known to date, extends from the central islands 

 of Samar, Leyte, Bohol, and Cebu, southward over Mindanao to Jolo 

 on the west and Sarangani and Palmas islands on the east in the Phil- 

 ippines, and still farther south beyond our range at least to Celebes. 

 A plotting of the known distribution points strongly to the fact that 

 many additional subspecies may be expected when more careful and 

 extensive collecting shall have been done. The species should occur 

 on the islands betw:een Samar, Leyte, and Mindanao. In Mindanao 

 itself we know it only from the northern coastal strip and Zamboanga 

 and it scarcely stands to reason that there should be a gap in the dis- 

 tribution between the north coast and the little islands of Sarangani, 

 Balut, Olanivan, and Palmas off the southeast coast where it is well 

 represented- 



