78 LEPAS HILLII. 



Extremely common ; attached to ships' bottoms, from all parts of the 

 world ; on floating timber ; associated with L. anatifera and L. anserifera. 

 Mediterranean. Attached to turtles, in the Atlantic, lat. 30° north. West 

 Indies. Falkland Islands. " South Seas/' collected by A. Menzies. Port 

 Stephen, Australia. 



General Appearance. — Capitulum laterally flat ; length 

 varies in proportion to the breadth; valves white, somewhat 

 translucent, moderately thick, very smooth, but with faint 

 traces of radiating lines ; in some varieties, surface rather 

 irregular along the zones of growth. Scuta without any 

 internal teeth, and with scarcely any trace of the internal 

 basal rim ; upper angle little acuminated ; the occludent 

 margins of the two scuta stand rather separate from each 

 other, showing a wide space of corium between them : these 

 margins are arched and protuberant, but with the lower 

 part a little hollowed out ; basal margin a little curved. 

 In one specimen alone, I saw a trace of a diagonal line of 

 square coloured marks, like those common in L. anatifera. 

 Terga rather broad, with the basal angle not much 

 acuminated. The degree of prominence and outline of 

 the double occludent margin varies very much. Carina, 

 separated by a rather wide space from the scuta and 

 terga ; of very varying shape, the upper part not much 

 acuminated, generally very flat, sometimes exteriorly 

 marked by a central depressed line ; never barbed ; 

 occasionally, (in a specimen from Australia,) middle part 

 so wide as almost to become spoon-shaped ; on the other 

 hand occasionally of nearly the same width throughout ; 

 somewhat constricted above the fork. Fork deeply 

 embedded as usual ; situated, in fresh specimens, a little 

 way beneath the basal margins of the scuta, instead 

 of touching them, as in the other species ; forks of vary- 

 ing width, not so abruptly inflected as in many species ; 

 sometimes much narrower than the upper widest part of 

 the valve, sometimes nearly twice as wide ; prongs of fork 

 not very sharp, diverging at about a right angle, with the 

 rim between them reflexed. The apex of the carina 

 extends up between the terga for barely half their length, 



