Part II. AMERICAN ACHATINIO. 



Genus OPE AS (continued). 



Opeas is represented in America by four species extending 

 over nearly the whole tropical region, and by a number of 

 local forms. Most of the American species do not differ 

 much from the Oriental forms, but one, 0. beckianum, has 

 short rounded whorls and a distinct umbilicus at all stages of 

 growth. A form of this species has been made the type of a 

 new genus, Synopeas, by M. Jousseaume. This might be re- 

 tained as a subgenus, yet it is 'connected with ordinary Opeas 

 by the intermediate species 0. micro,. The species are ar- 

 ranged as follows: 



Generally distributed forms, species 1 to 4. 



Antillean forms, species 5 to 8. 



South American forms, species 9 to 15. 



Central American and Mexican forms, species 16 to 23. 



SPECIES COMMON TO SOUTH AND MIDDLE AMERICA AND THE 



ANTILLES. 



The four common American Opeas are very distinct and 

 easily recognized, though their wide range and variability has 

 resulted in an extensive synonymy. 



beckianum. Umbilicate, stout, with closely coiled whorls. 

 Length 6.2 to 9 mm., with 8 to 9j/ 2 whorls. Surface more or 

 less ribbed. 



0. micra. Perforate, with very obtuse summit, more or less 

 ribbed on the spire, with 7 or 8 whorls in a length of 6 to 

 9 mm., diam. 2 to 2.7 nun. 



0. gracile. Perforate, slenderly tapering, closely arcuately, 

 striate, with l l / 2 to 8^2 whorls in a length of 9-11.5 mm. 



0. goodalli. Slender, minutely perforate, with straightly 

 conic spire, very arcuate strice and outer lip, and about 

 whorls in a length of 6 to 7 mm. 



(188) 



