lii PLACOSTYLUS. 



first vein of the vena cava. The vena cava bears a second large 

 vein which parts the two branches of the first branch of the peri- 

 cardia! vein. The general reticulation is faint, the veins mentioned 

 having no large branches. 



The free retractor muscles (of P. shongii, pi. 54, fig. 41, nat, size) 

 are arranged as in the American Bulimulidce. The right ocular 

 retractor band arising from the face of the columellar mwscle. 



The genital system (pi. 51, fig. 23, P. shongii) is characterized by 

 the very large size of the fleshy penis, at the distal end of which the 

 short retractor muscle is inserted, its distal termination being on the 

 lung floor. There is no internal papilla, but the walls are corrugated 

 above (fig. 24), and bear a pilaster below (fig. 25). The vas 

 deferens is imbedded in the superficial integument of the penis nearly 

 to the base of the latter. The vagina is moderately long. The duct 

 of the spermatheca is short, the uterus being fully double its length. 

 A muscle binds the spermatheca to the oviduct. In P. elobatus (pi. 

 51, fig. 22, after Semper) Semper found a similar system, except 

 that the penis and spermatheca duct are much shorter. P. seemanni 

 and P. fulguratus have similar genitalia, all three being Fijian 

 species. In P. porphyrostomus Fischer found the genitalia about as 

 in shongii* except that the vagina and spermatheca with its duct are 

 shorter. In P. scarabus the penis is shorter (J. de C., 1871, pi. 7). 



The jaw is strongly arcuate, thick and brown, composed of many 

 narrow plaits, converging toward the median line, the median plate 

 wedge-shaped. 



The radula is of the normal Helicid type. The central teeth have 

 a strong mesocone, and small ectocones or none. The laterals are 

 similar, but asymmetrical without an entocone. They gradually 

 change to marginals by splitting of the mesocone. The radula of 

 P. shongii I examined has about 20 lateral teeth on each side, fol- 

 lowed by about 10 well-developed marginals, bordered by perhaps a 

 dozen or more small irregularly developed and probably functionless 

 marginal teeth. Semper found 120 to 158 teeth in a row in the 

 Fijian species (PI. 60, fig. 13, P. fulguratus, after Semper). There 

 is a perceptible though not great difference in form between the 

 marginal teeth of the Placostyles of Fiji and those of New Caledonia, 

 Lord Howe Island and New Zealand. 



PlacostyJus is typically Bulimuline in nepionic sculpture, teeth, 

 jaw, kidney and free muscles. It raries from most American genera 



