234 BULLETIN 181, UlSnTEiD STIATEIS NAmOINlAlL MUSlEtJM 



APEROSTOMA (APEROSTOMA) COSTARICENSE (von Martens) 



Plate 32, Figures 16-18 



1876. Cyclotus quitenMs costaricensis von MiVktens, Jahrb. deutschen malak. 

 Ges., vol. 3, p. 254. 



Shell helicoid, covered by a thin golden-yellow periostracum. The 

 base bears a moderately broad chestnut-colored band, which fades 

 anteriorly into the basal color, which is a little darker than that of 

 the upper surface ; interior of the aperture bluish white. The nucleus 

 consists of 2 small, well-rounded, smooth turns; the postnuclear 

 whorls are inflated, strongly rounded; the last one is slightly flat- 

 tened below the summit and is marked by obsolete hairlike axial 

 riblets, which become much enfeebled on the last half of the last turn. 

 The last fifth of the last turn is slightly decurrent. Suture strongly 

 impressed. Periphery feebly angulated. Base narrowly umbilicated, 

 marked by the continuation of the axial ribs, which become fused and 

 slightly stronger on the umbilical wall. Aperture very oblique, sub- 

 circular with a decided auriculation at the posterior angle, which 

 bears a groove in its middle; peristome simple; the basal lip with 

 2 deep notches, one marking the outer limit of the umbilicus; the 

 inner lip is slightly thickened. The parietal wall is covered by a 

 moderately thick callus, which renders the peritreme complete. 



U.S.N.M. No. 321045 contains two specimens from the Kedfield 

 collection, apparently received from Gabb. They come from Costa 

 Kica. The largest of these, which we have figured, has 4.7 whorls 

 and measures: Height, 23 mm.; greater diameter, 31.7 mm.; lesser 

 diameter, 24.4 mm. Height of aperture, 14.9 mm. ; diameter, 15.3 mm. 



U.S.N.M. No. 524052 contains another specimen collected by M. 

 Valerio. 



The much smaller size of this species readily differentiates it from 

 A. (A.) cai'mioU. 



APEROSTOMA (APEROSTOMA) EXIGUUM, new species 



Plate 32, Figukes 10-12 



Shell small, depressed-helicoid ; the upper surface covered with a 

 golden yellow peristracum. There is a broad light zone immediately 

 above the periphery and a still broader dark zone immediately 

 below this; the rest of the base is a little paler than the upper sur- 

 face. Interior of aperture bluish white. The nucleus consists of 2 

 small, well-rounded, smooth turns. The postnuclear whorls are some- 

 what inflated, well rounded and marked by slightly wavy, well-de- 

 veloped axial riblets, which are about as wide as the spaces that 

 separate them. There is an impressed groove a little below the summit 



