464 SUPPLEMENT. 



ture ovate-oblique, slightly effused at the base, margins dis-united ; iuuer lip 

 oblique, rather siuuated ia the middle; outer lip acute, entire. 



Patella, p. 154. The common limpet makes oval pits in timber as 

 well as in chalk. Small individuals sometimes roost, habitually, on laro'er 

 specimens, and make an oval furrow on the shell. The surface on which 

 limpets roost, and some space around it, is often covered with radiating stria 

 not parallel like iho^e produced by their teeth on nuUipore. Mr. Gaskoin 

 has a limpet-shell incrusted with nullipore, which other limpets have rasped 

 all over. In M. D'Orbigny's collection of Cuban sheUs there is a group of 

 oysters {0. coruucopice), with a colony of the Hippomjx mitrula sheltered in 

 their interstices ; these limpets have not only fed on the nullipore with which 

 the oysters are incrusted, but have extensively eroded the epidermal layer of 

 shell beneath.* 



As to the CahjptrcBidcB generally, although furnished with lingual teeth 

 (fig. 248) like those of the animal-feediug Vehdina, and themselves mani- 

 festing carnivorous propensities (p. 151), it is difficult to understand how 

 they can travel in quest of food. 



The shape of some species of limpet is believed to vary with the nature 

 of the surface on which they habitually live. Thus the British Nacelln pel- 

 lucida is found on the fronds of the tangle, and assumes the form called 

 N. IcBvis, when it lives on their stalks. (Forbes.) The Acmtea testudinalis 

 becomes laterally compressed and is called A. alvea when it grows on the 

 blades of the Zostera (Gould) ; and Patella minlata of the Cape becomes a 

 new "genus" {Cymba, Adams, not Broderip) when it roosts on the round 

 stems of sea-weed, and takes the form called P. compressa. (Gray.) 



Tanystoma (tubiferum) Benson, 1856. Helicida, ^\xe\\\\k& Anastoma, 

 minute, umbilicated ; aperture disengaged, trumpet-like, toothed. Banks of 

 the Irawadi, above Prome. 



PFEiFfEKiA (micans) Gray. Helicidce. A Nanina without the mucus- 

 pore at the tail. Philippines. 



Spiraxis, C. B. Adams, 1850. Ti/pe, Achatina auomala, Pfr. Shell 

 ovate-oblong, fusiform, or cylindrical ; last whirl attenuated ; aperture nar- 

 row, right margin usually inflected, columella more or less contorted, base 

 scarcely truncated, furnished with a deeply-entering callous lamina. Distr. 

 30 sp. W. Indies, Mexico, Juan Pernandez. 



Janella, Gray, 1850 (not Grat. 1826). Sj/n. Athoracophorus (!) Gould. 

 Ti/pe. Limax bitentaculatus, Qnoy. Elongate, limaciform, covered by a man- 

 tle with free margins ; back grooved ; tentacles 2, retractile, rising within 

 the edge of the mantle ; respiratory orifice to the right ot the dorsal groove, 



* A similar circumstance has been noticed in the fresh-water Paludmce and Am- 

 pullaria, by Dr. Bland and Mr. R. Swift; in the absence of other food they devour 

 the green vegetable matter incrusting one another's shells, and in doing this remove 

 the epidermis, or even make holes in the shell. 



