atjbiculidje. 75 



formly greyish ; aperture furnished with three stronger teeth on 

 both sides ; left margin thicker ; mouth more contracted. Length 

 19, breadth 11 mill. (Rousseau). 



Scarabus crassidens, Hombr. fyJacq. Voy.Pole Sud, Zool. v. p. 40. 



pi. 10. f. 12-14. 

 Pythia crassidens, Pfr. Man. Auric, p. 99. 



Hub. Isle of Amboina. 



§ 4. Doubtful species. 



36 ? Pythia dibatata. 



Polydonta dilatata, Beck, Ind. p. 102. n. 9. 



" Scar, imbrium, Guer. Iconoqr. pi. 7. f. 6 ? ; Griff. Anim. Kingd. 



pi. 27. f. 1.— Philippine Islands." 

 Pythia dilatata, Pfr. Mon. Auric, p. 99. 



37 ? Pythia gibbosa. 



Polydonta gibbosa, Beck, Ind. p. 101. n. 3. 

 Pythia gibbosa, Pfr. Mon. Auric, p. 99. 



6. PLECOTREMA, H. and A. Adams. 



Shell ovate-conic, or rather fusiform, solid, usually grooved 

 spirally ; spire conic, acute ; aperture oblong - , contracted ; pa- 

 rietal plaits two, the lower of which is bifid or divided into 

 two branches ; columellar plait single ; peristome more or less 

 thickened, sometimes terminating in a varix, bearing within two, 

 or rarely three teeth. 



Plecotrema, H. and A. Adams, 1853, Proc. Zool. Soc. p. 120 ; 

 Gen. rec. Moll ii. p. 240. 

 Pfr. in Malak. Bl. 1854, p. 149 ; Mon. Auric, p. 99. 

 Lirator, Beck, Ind. p. 103? 



This genus has been founded by its authors upon several new 

 types, and is easily to be distinguished by good and constant 

 characters. Nevertheless the Auricula labclla, Desh., which is 

 referred to it by H. and A. Adams, a very imperfectly known 

 species, seems to belong rather to the genus Cassidula, if it be not 

 identical with C. Kraussi. 



The known species may be arranged thus : — 



A. "With the umbilicus open § 1. No. 1- G 



B. Rather imperforate § 2. - 7-13 



C. Aberrant species § 3. - 14 



e2 



