242 BtTLLETdN 181, TJNTTED STATES NIATEODMIAIL MUStEUM 



APEROSTOMA (APEROSTOMA) PORTOBELLENSE, new species 

 PlATE 34, FiGUKES 7-9. 



Shell sm,all for the group, depressed-helicoid. The early whorls 

 red, the last covered on the upper surface by a thin horn-colored perios- 

 tracum. There is a light supraperipheral zone and a dark area im- 

 mediately below the periphery on the base. The rest is horn colored ; 

 interior of aperture pale buff. The nucleus consists of about 2 small, 

 well-rounded turns. Postnuclear whorls well rounded, with a de- 

 pressed area a little below the summit. The postnuclear whorls are 

 marked by very slender, retractively curved, closely crowded axial 

 ribs, which become coarser and more distantly spaced on the last whorl. 

 Suture well impressed. Periphery slightly angulated. Base openly 

 umbilicated and marked by the continuation of the axial ribs, which 

 do not gain materially in strength on the umbilical wall. Aperture 

 subcircular, drawn into a moderately produced angle at the posterior 

 angle, which bears a groove in the middle ; peristome simple ; the outer 

 lip expanded and slightly reflected; the inner slightly thickened. 

 The parietal wall is covered by a thick callus, which renders the 

 peritreme complete. There is only an emargination in the parietal 

 callus. 



The type, U.S.N.M. No. 251434, was collected by E. A. Schwarz 

 at Porto Bello, Panama. It has 4.7 whorls and measures: Height, 

 21.5 mm. ; greater diameter, 35 mm. ; lesser diameter, 23.3 mm. Height 

 of aperture, 15.2 mm. ; diam,eter, 17.3 mm. 



U.S.N.M. No. 251427 was collected by August Busck at Porto Bello, 

 Panama. 



This species can readily be distinguished from all the other members 

 of the group by its small size. 



APEROSTOMA (APEROSTOMA) FULTONI. new species 



Plate 35, Figures 1-4 



Shell depressed-helicoid, chestnut brown, with a lighter zone at 

 the summit and a white zone immediately above the periphery. There 

 is a broad dark brown band covering two-fifths of the base inmiediately 

 below the periphery and a slender narrow band a little posterior to 

 the middle of the base. The rest of the base is yellow horn colored ; 

 interior of aperture bluish white, showing the banding within. The 

 nucleus consists of 2 small, well-rounded, smooth turns. The post- 

 nuclear whorls are strongly rounded with a depressed area imme- 

 diately below the summit. The postnuclear whorls are marked by 

 rather regular strong retractively curved ribs, which are about as 

 wide as the spaces that separate them. Suture strongly impressed. 

 Periphery obsoletely angulated. Base moderately broadly umbili- 



