GASTEROPODA. 543 



outer cusp prolonged ; 2d and 3d laterals, simple curved 

 or hooked-shaped. The mandible, No. 109, divided 

 in the centre, forms two plates of divergent denticu- 

 lations. 



Halioth tuberculatus (the Ear-shell), is a well-known 

 beautiful shell much used for ornamental purposes. The 

 lingual band, Plate V. No. 114, is well developed. The 

 medians are flattened out, recurved obtuse teeth ; 1st 

 laterals, trapezoidal or bearn-like ; uncini numerous, about 

 sixty, denticulate, the few first pairs are prolonged into 

 strong pointed cusps. Turbo marmoratus (the Top-shell). 

 After the outer layer of shell is removed, it presents a 

 delicate pearly appearance. The lingual band, No. 123, 

 closely resembles Trochus ; it is long and narrow, the 

 median teeth are broadest, with five recurved laterals, and 

 numerous rows of uncini, slender and hooked. A single 

 row only is represented in the plate. Cyclotus translu- 

 cidus, a family of operctdate land-shells, belongs to the 

 Gyclostomatidce. The teeth shown at No. 110, formula 

 3 • 1 • 3, are arranged in slightly divergent rows on a narrow 

 band ; they are more or less subquadrate, recurved, with 

 their central cusps prolonged. Cistula catenata, one of 

 the family Cyclophoridoe ; its band, No. 115, formula 

 2-1-2, shows teeth resembling those of Littorina, and 

 should certainly be separated from Cyclophorida?. It 

 would also seem that the teeth of Cyclostomatidce point to 

 a near alliance with the Trochidce; but this question can 

 only be determined by an examination of several, species, 

 when it may, perhaps, be decided to give them rank as a 

 sub-order. They are numerous enough ; the West Indian 

 islands alone furnish us with 200 species. 



Professor William Thompson, in his paper " On the 

 Dentition of British Pulmonifera," Ann. Nat. His. vol. 

 vii. 1851, pointed out that the length of the lingual band, 

 and number of rows of teeth borne on it, vary greatly in 

 different species. The rows, however, being closely set 

 are usually very numerous ; but it is among the Pul- 

 monifera we meet with the most astonishing instances 

 of large numbers of teeth. Limax maximus possesses 

 26,800, distributed through 180 rows of 160 each; the 

 individual teeth measuring only one 10,000th of an inch, 



