THE CYODOPHORID LAND MOLLUSKS OF AMEKICIA 221 



Subgenus Aperostoma Troschel 

 1847. Aperostoma Teosohei^ Zeitschr. Malak., vol. 4, p. 44. 



Aperostomine shells in which the heavy calcareous deposit of the 

 adjacent turns of the operculum are fused. This deposit is a little 

 higher on the inner edge of the turns. The shells have an entire 

 aperture and a peripheral band. Their sculpture consists of fine axial 

 riblets; sometimes malleations are present. The aperture is wider 

 than high. 



Type: Aperostoma (Aperostoma) hlcmchetiamwm (Moricand). 



Distribution : Costa Rica to eastern Brazil. 



The radula formula of A. {A.) Ze^ is 3 : 3 : 3 : 2. In A. {A.) gigan- 

 teum {B^eeve) , confmum (Sykes), and cardozi (H. B. Baker) the verge 

 is on the back of the neck behind the tentacles, traversed by a seminal 

 groove. A short terminal appendage is present. 



KEY TO THE SPECIES OF SUBGENUS APEROSTOMA* 



Upper surface malleateji. 



Upper surface conspicuously malleated. 

 Greater diameter more than 30 mm. 

 Rugosities coarse. 



Umbilicus very large umbilicatum 



Umbilicus narrow cumingi 



Rugosities fine paezense 



Greater diameter less than 22 mm. 



Greater diameter more than 19 mm. 



Rugosities closely crowded bogotense 



Rugosities not closely crowded simile 



Greater diameter less than 16 mm inconspicuum 



Upper surface not conspicuously malleated. 

 Greater diameter more than 39 mm. 



Periostracum dark chestnut-brown cingulatum 



Periostracum olive-brown veracochanum 



Greater diameter less than 31 mm allantayum 



Upper surface not malleated. 



Posterior angle of aperture auriculate. 

 Umbilicus coarsely axially ribbed. 



Greater diameter more than 38 mm dunkeri 



Greater diameter less than 34 mm. 



Periphery with a weak keel pailaense 



Periphery without a weak keel paezicolum 



Umbilicus not coarsely ribbed. 

 Peristome notched. 



Notches of basal lip 2, 



Height more than 23 mm. 



Greater diameter more than 40 mm carmioli 



Greater diameter less than 34 mm costaricense 



Height less than 16 mm exiguum 



»We believe that A. (A.) inca (Orbigny) and filoUratum (Sowerby) belong in this sub- 

 genus, but having seen no specimens and having only poor illustrations we refrain from 

 attempting to place them in the key. 

 428349^ — 42 15 



