21 



irregular growth. They are cancellated near the top, but so little that it is hardly discernable 

 through a strong lens. Interstices at the top very finely transversely striated, becoming anteriorly 

 smooth and brilliant with growth striae only and a few indistinct longitudinal threads. In the 

 longest individual the peristome was often broken as it seems and each time the fracture was 

 repaired in such a wa)- that the ribs in their continuation alternate with the intervals. 



Apex without slit or notch, octagonal ; anterior aperture circular, not oblique. 

 a. Length 29 mill., greatest diam. 2 mill. 

 d. Length 33 mill., greatest diam. 2 mill. 

 c. Length 37 mill., greatest diam. 2,3 mill. 



Remarks. In ontward appearance D. oryx and D. leticoryx strongly resemble each 

 other. Both species are .slender, much attenuated, and show the same irregularity of growth. 

 It is moreover possible that in older specimen of D. Iciicoryx tertiary riblets yet might appear. 

 The difference lies in D. oryx being straighter than D. Iciuoryx and having a distinct!\- 

 octagonal anterior aperture. 



Group of D. BISEX.\XGUL.\TUM. 



.Six to fourteen ribbed at and near the apex. 



I. Six to twelve ribs at and near apex; the ribs sometimes longitudinally 



splitting. Length :h 30 mill. 8 or 9 times the diam intercalatum. 



II. Nine to eleven ribs at and near apex; the ribs sometimes longitudinally 



bisected. Length 30 — 50 mill. about 8 times the diam macandrewi. 



III. Nine ribs at and near apex. 



a. Interstices with secondary riblets. Length 33 mill., about 13 times the 



greatest diam sinuosum. 



a' . Interstices smooth. Length 20 mill. greatest diam. about 2,5 mill. . roèustum. 



IV. Eight to ten ribs, becoming obsolete toward aperture. 



a. Length 50, greatest diam. 4 mill lessoni. 



a' . Lenght 60, greatest diam. 3,5 mill pluricostatiun. 



V. Ten ribs at and near the apex. 



Interstices flat, finely transversely striated. Length 20, greatest diam. 2,5 mill. decemcostatum. 

 Interstices concave, finely ribbed. Length about 14 mill., greatest diam. 



1,7 mill. (sometimes eight-ribbed) tasmaniense. 



VI. Eleven to thirteen ribs; interstices with a weak thread or none. Length 70, 



greatest diam. ± 6 mill bisexangulatmn. 



MI. Eight to fourteen ribs. 



a. 14 ribs near apex. Length 31 mill. greatest diam. 1,6 mill. . . . cookei. 

 a' . 8 — 14 ribs at apex, intercalation of secondary riblets. Length ± 15 mill. 



greatest diam. 2 mill paucicotitoriuin. 



