412 PROCEEDINGS OF THE ACADEMY OF [July, 



inferior lamella strongly spiral within, calloused below; subcolu- 

 mellar lamella dilated adjacent to the very long and strong lower 

 palatal plica, which is united with the lunella, when that is pres- 

 ent; principal plica long; upper palatal plica developed, sometimes 

 coalescent with the lunella. 



The shell in this section is similar to that of the group of C. 

 ptychochila in general characters, but differs in the dilation of the 

 subcolumellar lamella and in the much higher, simple spiral plate 

 of the inferior lamella within the last whorl. Like the group 

 mentioned, its peculiarities are an exaggeration of the platydera 

 group of Hemiphcedusa, which may be looked upon as a sort of 

 unspecialized branch of the common stock. The clausilium, how- 

 ever, is so peculiar and unlike any Phsedusoid group hitherto 

 known, that the erection of a new section is required. The 

 lamellae and plicae are all very strongly developed within, and the 

 former are unusually long, passing the ventral position. 



Luchuphcedusa has much in common with the section Emargina- 

 ria Bttg. of the German upper Miocene, in which a similar emar- 

 ginate or notched clausilium and the same interlamellar plication is 

 developed ; but the Miocene forms retain a primitH e structure of 

 the palatal region, where several plicae are developed, while Jjuchu- 

 phcedusa is very highly specialized there. The resemblance is par- 

 tially due to convergent evolution. 



Key to species of Luchuphcedusa, by external characters. 



1. Right margin of the peristome crenulate: 



a. Aperture narrow, the sinulus strongly developed; princi- 

 pal plica reaching to the lip; last whorl strongly com- 

 pressed (Oshima). 



b. Subcolumellar lamella wholly immersed (though the 

 lip is crenate at its position), ... 0. oshimce. 

 6'. Subcolumellar lamella emerging to the lip-edge, 



C. pseudoshimce. 

 a'. Aperture moderately wide, of normal proportions, piri- 



form-ovate ; principal plica immersed, as usual. 



b. Rather large, the broad right lip deeply plicate ; 



length about 23 mm. (Okinawa), C. eallistochila. 



b'. Small, length about 12 mm. : the right lip narrow 



and not very strongly crenate (Oshima), (7. mima. 



2. Right margin of the peristome smooth; aperture semicircular; 



inferior and subcolumellar lamellae emerging to the lip-edge; 



length 30-34 mm. (Oshima), .... (7. nesiothauma. 



