144 SYSTEMATIC ARRANGEMENT 



b. Imperatorina. Body subquadrate. Aperture of shell subqua- 

 drate. Operculum oblong or ovate, solid, convex. Shell top- 

 shaped ; front of whorls flattened. 



9. UvANILLA. 



Operculum flat, with two distinct convex radiating ribs, lower one 

 straight and nearly parallel to the edge, upper arched, subcentral ; 

 axis imperforate, callous. Shell top-shaped, imperforate, with mar 

 ginal spines. 



1. U. olivaceus. Trochus o., Gray. 



2. U. unguis. Trochus u., Gray. 



3. U. fimbriatus, t. 38. f. 9. 



10. Calcar. 



Operculum thick, with a slight convexity over the axis ; outer 

 edge thin ; axis perforated. Shell top-shaped, imperforated ; whorls 

 keeled, with spiny scales. 



1. C. magnus, Chemn. Trochus Calcar, Linn. 



2. C. stellaris, t. 39. f. 4. 



11. Pomaulax. 



Operculum flat, with three convex radiating ribs ; upper submar- 

 ginal ; axis perforated. Shell trochiform, imperforated ; whorls 

 nodulose behind. 



1. P. undosus. Trochus u., Gray. 



2. P. japonicus. Trochus j., Bunker. 



12. GUILDFORDIA. 



Operculum flat, with a very slight ridge near the arched or outer 

 margin. Shell depressed, with elongated marginal spines ; outer 

 lip sinuous ; axis covered with a callus. 



1. G. triumphans. Trochus Guildfordiae, Gray. 



2. G. heliophorus, t. 40. f. 1 . 



13. Pachypoma. 



Operculum oblong, subquadrangular, very convex externally. Shell 

 top-shaped, imperforated ; pillar-lip rather truncated in front. 



1. P. insequalis. Trochus i., Martyn. Trochus gibberulus, Chemn. 



2. P. cselatus. Trochus c, Gmelin. 



14. Lithopoma. 



Operculum ovate, thick, thicker at the end, with a broad thin 

 margin on outer edge. Shell top-shaped, imperforated ; whorls 

 nodulose ; aperture subcircular. 



1. L. tuber. Trochus t., Linn. 



