INTRODUCTION. 



Family ACHATINELLIDJ3 Tryon. 



Achatinellida Tryon, 1884 (exclusive of Tornatellinida and 



Amastrida). 



Orthurethra with the kidney longer than the pericardium, 

 oblong and narrow. Surface of the lung plain. Genitalia 

 complicated by the presence of a long appendix provided with 

 a branch from the penial retractor muscle. Spermatheca em- 

 bedded in the prostrate gland, its duct long and simple ; albu- 

 men gland minute; prostate gland enormously developed, 

 composed of vermiform caeca. Jaw wanting or extremely thin, 

 indistinctly plaited vertically. Radula broad and short. 

 Teeth excessively numerous, arranged in V-shaped transverse 

 rows ; rake-like, composed of a narrow basal plate and a broad 

 recurved portion bearing numerous unequal cusps. 



The shell is more or less glossy, dextral or sinistral, oblong 

 or ovate, minutely perforate or closed, composed of five to 

 seven whorls, the last convex ; aperture ovate ; outer lip thick- 

 ened or simple, sometimes expanding a little; columella usu- 

 ally bearing a strong, obliquely entering lamella in the last 

 whorl; internal axis sinuous. No entering lamella or tooth 

 on the parietal wall. Animal externally as in Helicidce. Foot 

 moderately broad, usually shorter than the shell. Viviparous.. 



Distribution, the Hawaiian Islands (except Kauai, Niihau 

 and perhaps Kahoolawe). Living on trees and other plants. 



Studies of the soft anatomy with abundant material have 

 demonstrated, in my opinion, that the Achatinellidcz and 

 Amastrida are strongly distinct families. None of the many 

 species of both, dissected by other naturalists or by myself, 

 show the slightest approach in their differential characters. 



The Achatinellidce in essential structure stand nearest to 

 the Amastridcr, Enidce and Ferussacida, and are somewhat 



(ix) 



