14 UNITED STATES NATIONAL MUSEUM BULLETIN 2 96 



view that they are involved primarily in holding the mantle outward 

 against the shell. 



The inner surface of the mantle generally is smooth, except for the 

 area surrounding the mantle aperture, where hairs and the comb 

 collar usually are found. 



The principal structure in this area is the comb collar, which 

 consists of a thin membrane lining the inner surface of the mantle 

 near the aperture, and extending into the aperture itself. The mem- 

 brane is minutely folded with the anterior or apertural ends dissociated 

 into an extremely delicate row of fringed hairs (fig. 2c). The comb 

 collar extends from one side of the aperture to the other. It may 

 extend along most of the aperture, or be confined to the ventral end 

 away from the attachment end. Often it is folded inward between the 

 paired thoracic cirri, or outward from the aperture as a separate 

 velum, e.g., as described in Berndtia purpurea by Utinomi (1957, p. 7). 



In addition to the comb collar, the mantle aperture frequently is 

 guarded by an array of hairs distributed in patches. An internal 

 lateral bar has been described for Balanodytes taiwanus (Utinomi 

 1950b). 



Another special feature of the mantle interior includes fleshy 

 projections in the genus Trypetesa. Utinomi (1964) describes a series 

 of finger-like processes in T. habei, while Darwin's description (1854) 

 of T. lampas, and my description (Tomlinson 1953) of T. lateralis 

 describes two internal mantle flaps. These are probably respiratory in 

 nature, and may have something to do with a brood function in the 

 latter two species. 



The mantle itself is laced with muscle strands, and contains the 

 ovary in the dorsal portion. These are discussed under the separate 

 headings, Muscular System (page 22) and Reproductive System (page 

 24). 



External Mantle Flap in Trypetesa lateralis 



Penetration and Male Incidence 



An external mantle flap, strongly equipped with boring teeth, 

 appears on mature females of T. lateralis. It burrows away from the 

 female in an arc, and finally perforates to the outside of the shell with 

 a very small, slit-shaped opening. 



That the perforations are necessary for some process is supported by 

 the great lengths to which the animal will go to establish this per- 

 foration to the outside. Flaps two-thirds as long as the entire barnacle 

 are not uncommon for barnacles in some positions within the shell 

 (e.g., within the columella). 



