TOBNATELLIDES OF HAWAIIAN ISLANDS. 223 



little below the periphery, narrowly rounded basally. The 

 aperture is small, oblong. Parietal lamella reduced to a mere 

 thread. Columella unarmed, its margin dilated. Umbilicus 

 large, contracting slowly within. Length 4.6, diam. 2.2, length 

 of aperture 1.5 mm. 



Molokai : Moomomi, at base of the bluff and up to about 

 600 ft. ; also back of the dunes, about a quarter of a mile in- 

 land; fossil in the calcareous sands (Cooke & Pilsbry). Type 

 no. 112534 A. N. S. P., cotypes in B. P. B. Mus. 



This species has the straight contour and flat whorls of the 

 T. cyphostyla group and of Tornatellaria. It is distinguished 

 by the extreme reduction of the parietal lamella, and the ab- 

 sence of columellar lamellae, from at least the mid-neanic 

 stage on. Whether these lamellae are present in younger 

 stages has not been ascertained. 



Group of T. perkinsi. 



Tornatellides with abrupt, almost truncate basal contour 

 (though the base itself is convex), conical spire and closely 

 coiled whorls. The parietal lamella of adults is usually very 

 low, not over 0.1 mm. in height; in immature specimens it 

 varies from nearly twice to three times the height of the 

 lamella of adults. The columella is furnished with two nearly 

 equal, almost transverse folds, which are visible through the 

 umbilical wall and are not strong in the adult stage. In 

 immature specimens the lower columellar fold is somewhat 

 stronger than the upper. In most of the species the umbilicus 

 is remarkably large, but in perkinsi, frit and micromphala it 

 is small. 

 a. Umbilicus large, more than 0.5 mm. in diameter. 



&. Adult shells with the diameter less than 57% of the 

 length. 



c. Adult shells not over 3.3 mm. in length and 

 with less than 7*4 whorls. 



T. macromphala, no. 34. 



c 1 . Adult shells more than 3.5 mm. (usually about 

 4 mm.) in length and with more than iy 2 

 whorls. T. productus, no. 33. 



