86 MONODONTA. 



L. c. p. 160, no. 33. 



CLANCULUS ZEBRIDES A. Adams. C. testa conoidea, fuscesceni, 

 nigro-fusco radiatim picta, cingulis grauorum sculpta ; intersititiis 

 lineolis transversis elevatis ; anfr. rotund atis ; umbilici margine 

 crenulata ; columella supra tuberculo, margine callosa, basi tuberculo 

 magno terminate ; labro intus dentibus linearibus instructo. 



Habitat unknown. 



L.c.p. 161, no. 39. 



Said by Tenison- Woods to be the same as C. variegatus A. Ad. 



Genus MONODONTA Lamarck, 1801. 



Monodonta LAM. Syst. des. An. s. Vert. p. 87 (1801). GRAY, 

 Syst. Dist. Moll. Brit. Mus., p. 155. A. AD. P. Z. S. 1851, p. 173. 

 H. and A. AD., Gen. Rec. Moll, i, p. 417. WOODWARD, Manual of 

 Moll. p. 144.^-FiscHER, Man. de Conchyl., p. 820. Labio OKEN, 

 Lehrbuch, p. 263, and some other authors. Monodontes MONTF. 

 Conch. Syst. ii, p. 195. Trochidon SWAINS. Treatise on Malacol. p. 

 351. Odontis SOWERBY, Cat. Tankerv. coll. p. 53. Trochulus 

 HUMPH. Monodon SCHWEIGGER. 



The genus Monodonta was first separated from the Linnseau genus 

 Trochus by Lamarck in 1801, T. labio L. being given as the type. 

 Later, Lamarck included many species of such dissimilar groups as 

 Tectarius, etc ; but modern authors have restricted the genus to the 

 toothed Trochids allied to the type. 



Monodonta consists of globose-conoidal shells with more rounded 

 body-whorl and aperture than Trochus. With the exception of 

 several forms from the West Coast of S. America, the species are all 

 Old World in distribution, mostly tropical. All are littoral. Geo- 

 logically, the genus dates from the Trias. The prominent character 

 of the dentition (pi. 50, figs. 5, 12) is the development of the lateral 

 basal angles of the central and lateral teeth into broadly projecting 

 lobes imbricating over the adjacent tooth ; the cusp of the central is 

 wide, shortly reflexed, its edge denticulate at the sides, smooth in 

 the middle. 



Subgenus MONODONTA Lam. 

 Section Monodonta (restricted). 

 M. LABIO Linne. PL 19, figs. 95, 96. 



Shell imperforate globose-turbinate, very solid, grayish-pink or 

 greenish, mottled or longitudinally striped with purplish-red or 



