136 PHASIS-TRACHYCYSTIS. 



The name Phasis is said by Agassiz (Nomencl. Zool.) to have 

 been used by Hiibner in 1816 for a genus of Lepidoptera, but the 

 name was used for a species not a genus. See Zutriige zur Samml. 

 exot. Schmetterl. p. 41 (1818). 



Section TRACHYCYSTIS Pilsbry. 



Pella ALB. (in part), Die Hel., edit. Martens, p. 84 (1860), type 

 H. bisculpta Bens. Not Pella Steph., Illustr. Brit. Ent., Mandibu- 

 lata, vol. v, p. 434 (1832), a valid genus of Coleoptera. 



Small shells, generally thin, somewhat translucent, horny or 

 earthy brown in color, usually sculptured with fine oblique riblets; 

 the lip simple and thin, dilated at the columellar insertion ; umbili- 

 cus generally narrow. 



These forms are evidently allied to Phasis in the dilated colu- 

 mella, etc. They have the appearance of some of the New Zealand 

 Patuloid Helices, but the foot lacks parapodial grooves and caudal 

 mucous pore. The jaw is ribbed ; and the group is probably to be 

 regarded as an odontognathous genus of the Haplogona of my 

 arrangement of the Helices (Proc. Acad. Nat. Sci. Phila. 1892). 



The following forms should be added to those described in Vol. 

 III. See above, under Pella, for species to be removed to other groups. 



Group of H. browning ii. 



P. BROWNINGII Benson. Vol. IX, pi. 6, figs. 1, 2, 3. 



Shell narrowly umbilicated (the width of the umbilicus contained 

 8J times in the diameter of the shell}, rather depressed, thick lens- 

 shaped ; thin, -horn-colored, subtranslucent below, having radiating 

 streaks above and below of light brown, and close regular white rib- 

 lets above ; surface shining. 



Spire low-conoid with slightly convex outlines and stibobtuse but 

 not flattened apex ; suture moderate, crenulated. Apical whorl 

 smooth, corneous, the next half whorl having fine, delicate stria?, 

 the following whorls sculptured ivith oblique, regular , thread-like rib- 

 lets, which are white and slightly curved, numbering on the body 

 whorl at periphery about 57. These riblets are slightly strengthened as 

 they pass over the peripheral angle, which is beautifully crenulated 

 by them ; but immediately below this they become thin and delicate, 

 mostly lose their white color, and to the naked eye disappear ; but 

 under a lens they may be seen continuing to the umbilicus. 



