32'4 MANUAL OF TTiE MOLLUSCA. 



Iries of growtli ; apex sub-central, oblique, scarcely raised ; 

 rr.argins acute ; inner surface with a central coloured and 

 striated disk, surrounded by a continuous irregular muscular 

 impression. It bas a minute sinistral nucleus. 



Animal witb a very large tuberculated foot, deeply notched 

 in front ; mouth small, proboscidiform, retractile into the pedal 

 notch, covered by a small-lobed veil ; dorsal tentacles ear- 

 shaped, with large plicated cavities at their bases ; eyes small, 

 sessile between the tentacles ; mantle not extending beyond the 

 shell ; gill forming a series of plumes beneath the shell in front 

 and on the right side ; reproductive organ in front of the dorsal 

 tentacles ; excretory orifice posterior, tubular. 



Bistrihuti'on, 6 species. Canaries, Mediterranean, India, China, 

 Sandwich Islands. 



Fossil, 4 species. Oolite — . United States, Sicily, Asia. 



Tylodina, Eafinesque. 



Type, T. punctulata, Eaf. (= citrina, Joannis). 3 species. 

 Mediterranean, Norway. 



Fossil, 1 species. Tertiary. 



Shell limpet-like, depressed, apex sub-central, with a minute 

 spiral nucleus. 



Animal oblong, foot truncated in front, rather pointed 

 behind; dorsal tentacles ear-like, with eyes sessile at their 

 inner bases ; oral tentacles broad ; branchial plume projecting 

 posteriorly on the right side. 



Family Y. — Phyllidiad^. 



Animal shell-less, covered by a mantle, branchial laminae 

 arranged in series on both sides of the body, between the foot 

 and mantle. Sexes united. 



Phyllidia, Cuvier. 



Type, P. pustulosa, Cuvier. 



Etymology, diminutive of phyllon, a leaf. 



Animal oblong, covered with a coriaceous tuberculated 

 mantle ; dorsal tentacles clavate, retractile into cavities near 

 the front of the mantle ; mouth with two tentacles ; foot 

 broadly oval ; gills forming a series of laminae extending the 

 entire length of both sides; excretory orifice in the middle 

 line, near the posterior end of the back, or between the mantle 

 and foot ; reproductive organs on the right side ; stomach 

 simple, m'embranous. 



Distribution, 5 species. Mediterranean, Eed Sea, India. 



