122 THE NAUTILUS. 



A NEW SPECIES OF SEGMENTINA. 



BY BKYANT WALKER. 



SEGMENTINA CRASSILABRIS n. sp., PI. VII, figs. 4-6. 



Segmentina wheatleyi, Witter, J. of Conch., I, 388 (1878). 

 ' ? Walker, Naut. VI, 137 (1893). 



Walker, Rev. Mich. Moll., 18 (1895). 



Shell dextral, broadly umbilicate, planorboid, smooth, slightly 

 wrinkled by subobsolete growth lines and microscopic transverse 

 lines and undulations ; light horn colored ; whorls 4^, regularly in- 

 creasing, those of the apex flattened and concavely depressed, ante- 

 penult and body whorl rounded above, the latter deflected and slightly 

 expanded towards the aperture, and sharply contracted at the lip, 

 forming an obtuse crest just behind the edge of the lip, obtusely 

 angled below, around the deep, subfunicular umbilicus ; aperture 

 oblique, subtriangular, greatly contracted by a heavy callous 

 ridge just within the lip, the face of which is concave, the edge of 

 the lip being sharp and black ; the extremities of the labial ridge are 

 connected by a slight callus across the parietal wall ; apertural 

 lamellae six ; two parietal and four (palatal) on the outer wall. 

 The principal parietal lamella is a thin, broad, sigmoid blade rising 

 from the lower third of the parietal wall, and extending upward and 

 backward nearly to the suture, it is widest in the center, the ante- 

 rior extremity is subtruncate and rather abruptly bent outwards, 

 posteriorly it slopes gradually to its termination ; below this and 

 just behind the curve in the anterior portion and about halfway be- 

 tween it and the base is a short, sharp denticle projecting obliquely 

 forward and downward ; the lower palatal fold extends transversely 

 nearly across the entire base of the whorl and is a low, strong fold, 

 the upper surface of which is parallel with the base, the inner ex- 

 tremity is opposite the lower parietal lamella and rises abruptly at 

 right angles to the base, the outer extremity is rounded and bent for- 

 wards, sloping down to its termination, viewed externally the base of 

 this fold roughly resembles a figure-7 ; immediately above this, 

 about halfway between it and the lower extremity of the third pala- 

 tal fold, and about at the periphery of the whorl is a short, trans- 



