126 PTERODISCUS. 



appearance of spiral striation, produced by spiral bands of 

 microscopic, radially arranged wrinkles, visible on the last 

 part of the first whorl, and the first half of the second. 



5. P. REX (Sykes). PL 24, figs. 7, 8. 



"Shell much depressed, heliciform; umbilicus deep, of 

 moderate size; dark horn-color, strongly rugosely striated, 

 with a fairly large protoconch; whorls five, increasing regu- 

 larly, plano-convex, the suture being impressed and well 

 marked ; the last whorl is carinate, flattened above and some- 

 what inflated at the base ; at the periphery the periostracum 

 is exaggerated into a produced layer, from which projections 

 in the shape of arrow-heads arise at right angles to the 

 periphery ; mouth subquadrate, with the lip hardly thickened 

 and not reflected ; columellar plait fairly strong and horizontal. 

 Diam. maj. (with the peripheral wing) 14.5, alt. 4' mm." 

 (Sykes). 



Summit of Konahuanui, Oahu, Hawaiian Islands, amongst 

 dead leaves and moss. This very interesting shell was col- 

 lected by Mr. Ernest Lyman, and was kindly sent to me by 

 Prof. H. W. Henshaw. 



Amastra (Kauaia) rex SYKES, Annals and Magazine of 

 Natural History, ser. 7, vol. xiv, August, 1904, p. 159, wood- 

 cuts. 



"It somewhat recalls in form and appearance the well- 

 known Helicina agglutinans, the periostracum covering the 

 shell and being produced into an uneven wing at the periph- 

 ery, some of the projections extending to 2 mm. from the 

 shell. The species belongs to the group of Amastra alata, 

 Pf r., and A. heliciformis, Ancey ; from the latter, which is 

 also an Oahu shell, it may readily be separated, in addition to 

 its greater size and remarkable development of periostracum, 

 by its more depressed form and smaller (proportionally) 

 umbilical area." (Sykes). 



A form which seems probably referable to P. rex was taken 

 by Mr. D. Thaanum in Kalihi, a valley west of Nuuanu. The 

 umbilicus is much smaller than in P. wesleyi, contained about 

 61/2 times in the diameter, angular at its opening, conic 



