150 UNIVALVES TURBO. 



class : the T. margaritaceus and T. argyrostomus are 

 remarkable for the delicate coloring of their mouths. 



The T, delphiniis may be adduced as an example of 

 the species of the fourth division. 



The fifth division contains some of the most beautiful 

 species of the g-enus: they are in general thin and trans- 

 parent, and strongly marked by rows of elevated conti- 

 nuous ribs. The T. scalaris (the True Wentle-trap*), on 

 account of its beauty and rarity, deserves a particular 

 description. The shape of the shell (which is extreme- 

 ly elegant) is a spiral cone, formed by gibbous whorls, 

 gradually decreasing from the base to the apex, un- 

 connected by a columella ; this circumstance, so com- 

 pletely opposed to the regular structure of other turbi- 

 nated shells, has occasioned considerable doubt as to 

 its classification, and some authors have even placed it 

 among the Serpulae. The whorls are divided, at re- 

 gular distances, by rows of elevated, suboblique, 

 longitudinal ribs, which in young shells have a semi- 

 pellucid appearance. The color is usually a yellow- 

 ish or brownish white. The T. clathrus, or False Wentle- 

 trap, is a very common shell, and much more taper 

 and elongated than the T. scalaris. It has no umbilicus, 

 and the Avhorls are closely united. 



The sixth division greatly resembles the preceding in 

 form, and is only distinguished by its whorls not being 

 surmounted with elevated cancellations. 



* Wentle-trap is derived from a German word, Wiiidle-treppe, 

 signifying a winding stair-case. 



