20 PLACOSTYLUS. 



Placostylus KOBELT, Syst. Conchyl. Cab. Mart, and Chemn., edit. 



2 (monograph) HEDLEY, The Range of Placostylus; a study in 



ancient geography, Proc. Linn. Soc. N. S. Wales (3), vii, 1893, p. 

 335 ; and A Zoogeographic Scheme for the Mid-Pacific, Proc. Linn. 

 Soc. N. S. W., 1899, p. 391 (distribution). 



Melanesian Bulimulina with thimble-punctate nepionic whorls, 

 and ovate or oblong, dextral, usually perforate shell, solid or ponderous 

 and dark brown in the terrestrial species, thin and paler or variegated 

 with zigzag streaks in the arboreal ; often spirally malleated or 

 corrugated. Aperture ovate or ear-shaped, frequently of a charac- 

 teristic orange-red color; the outer lip blunt and unexpanded or 

 reflexed, with a tendency to become abruptly narrower above; colu- 

 mella generally with a spiral fold, often calloused; parietal wall cal- 

 loused and bearing a tooth, or simple. 



Type P.fibratus Martyn. 



A genus comprehending species quite diverse in appearance, often 

 cannot be diagnosed from the shell alone, even when the general as- 

 pect is characteristic. Most Placostyli have a brown olive or green- 

 ish cuticle, but in some it is white, in others wanting. The particular 

 tone of red-orange of the aperture is very characteristic when devel- 

 oped, but is wanting in many species. The shallow sinus of the 

 outer lip posteriorly in the region of the lung-pore and anus, is a 

 prevalent tendency, but imperceptible in most of the thinner species; 

 and the apical punctation is generally worn off in the larger species, 

 and indistinct in a few small forms. 



The affinities of the group are nearest with Bothriembryon. The 

 resemblance to Partula noticed by Dr. Kobelt and others is purely 

 superficial, and does not indicate the relationship claimed by these 

 authors. 



The earlier monographers had but few species of this genus, the 

 monograph by Kobelt in the Conchylien Cabinet, 1891, being the 

 only one worthy of especial mention. The materials for a mono- 

 graph were largely brought together by Crosse, who has compiled 

 several very useful catalogues. Kobelt's work includes most of the 

 species, which are described and figured in his usual careful manner ; 

 but it is marred by the total absence of classification, either biologic 

 or geographic ; the result being that closely allied forms are scat- 

 tered at wide intervals through his pages and plates. 



The distribution of Placostylus has been the subject of an able 



