2 TROCHOMORPHA. 



In T. castra and T. timorensis (pi. 9, fig. 31) the duct of the sper- 

 matheca is very long. In all other features of genitalia, jaw and 

 teeth, they resemble the typical Trochomorphas. The length of this 

 duct may warrant the retention of the section Sivella Blanf. 



Jaw arcuate, smooth, with a small median projection, or none. 

 (PL 8, fig. 10, T. assimilis; pi. 7, fig. 13, T. planorbis ; pi. 9, fig. 30, 

 T. timorensis.) 



Radula : Central and lateral teeth having the strong mesocones pro- 

 jecting well over the posterior borders of their basal-plates, and lacking 

 ecto- and entocones. Outer lateral teeth at first siuuated outside, the 

 sinuation increasing to a denticle on the transition teeth, and 

 ascending on the mesocone to form the long bifid cusps of the marginal 

 teeth, which become very oblique (pi. 8, fig. 11, T. assimilis, central, 

 lateral and transition teeth, with several adjacent marginals and an 

 outer marginal drawn). See also fig. 18, T. subtrochiformis, show- 

 ing central and 1st, 12th, 13th and 24th teeth. 



Of the names quoted in the reference paragraph above, none ante- 

 dates Trochomorpha except v. Hasselt's Geotrochus, dating from 

 1823 ; but as the species included by the Dutch author were not 

 described nor figured, and in fact remained unrecognized until v. 

 Martens identified them by the aid of v. Hasselt's unpublished 

 drawings, his names cannot have precedence for either genus or 

 species. 



The prominent features of this genus are its simply conical or 

 lens-shaped, smooth shell, with toothless aperture and non-expanded 

 lip ; the undivided sole of the foot, bordered above by parapodial 

 grooves, without caudal mucus gland; the simple genitalia; smooth 

 jaw ; and unicuspid central and lateral, and bifid, Nanina-like mar- 

 ginal teeth. 



Our knowledge of the anatomy of this genus hitherto has been 

 due to Semper's investigations. Gould has given figures of the liv- 

 ing animal of tentoriolum, troilus and conijormis, and Quoy and 

 Oaimard figure that of solarium. All of these figures agree with my 

 own observations and figures of T. assimilis Grt., from which the 

 above account is mainly drawn. Wiegmann has recently dissected 

 a specimen of T. planorbis Less. (Webers' Zool. Ergebnisse einer 

 Reise in Niederliindisch Ost-Indien, iii, p. 152, 1893). This species 

 shows the lower portion of the vas deferens to be dilated beyond the 

 apex of the penis, where the retractor muscle is inserted (pi. 7, figs. 

 14, 15, showing penis, etc. from both sides). The vagina is much 



