HELICOSTYLA. 217 



oral, with a very short duct, its thick wall composed of radially 

 arranged follicles (pi. 54, fig. 7, longitudinal section of mucus 

 gland of H. butleri). Dart short, straight, and round in section. 

 Spermatheca oval, on a long, branchless duct (pi. 54, fig. 8, H. but- 

 leri; pi. 54, fig. 9, H. pit hog aster with its dart). 



Distribution: Philippine Is., with a few species in the Moluccas, 

 in New Guinea and the Solomon Islands. Habits mainly arboreal. 



As in most large genera of Helices, the shells of Helicostyla 

 exhibit a very wide range of forms, some being heavy, dark, de- 

 pressed and keeled, others globose and thin with brilliant green or 

 variegated coloring, while still other species are of an elongated 

 Bulimus-like contour. Peculiar air-permeated cream-white epider- 

 mal bands and patches are characteristic of many but by no means 

 all species, and in most the columella is solid. 



The jaw is of the usual ribbed type. The teeth are like those of 

 some Papuinas, but in the lack of side cusps on middle and lateral 

 teeth they resemble Eulota. The genital system is highly charac- 

 teristic in the globose form of the mucus gland, which as in other 

 Belogona euadenia is inserted on the dart sack. In the subgenus 

 Canistrum (q. v.) a variation in this is found. Our knowledge of 

 the anatomy is due to Semper, whose work upon the group leaves 

 little to be desired except the examination of those subgenera 

 which he did not dissect, Prochilus, Chrysallis, Pap'iistyla, Crystal- 

 lopsis, etc., and the further investigation of Canistrum find allied 

 forms. 



It is clear that Helicostyla is very near in anatomy to the primi- 

 tive Belogonous stock, retaining early characters in the simple un- 

 split and nearly sessile mucus gland and needle-like, bladeless dart. 

 Its differentiation in shell characters is attributable to long isolation 

 and the assumption of arboreal habits. The Philippine Chlorseas 

 were probably derived from a later incursion or an early split, 

 which has not spread through the entire Philippine group. The 

 (hmcena, Euhadra and Eulota forms are perhaps to be regarded 

 as a more recent addition to the fauna. 



The subgenus Helicostyla was proposed by Ferussac for a hetero- 

 geneous assemblage of shells including certain Zonitidce, two Sagdas 

 and a Gastrodonta, the two species of Stylodonta, Cepolis (Coryda) 

 alaada and H. mirabilis and coniformis. The Sagda and Gastro- 

 donta were later removed from the group by Ferussac himself 

 (Tabl. Syst., p. 67) ; and Beck in 1837 eliminated from it most 



