64 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 37. 



a^ Stalked or pedunculate barnacles. 



6\ Peduncle scaly ; capitulum composed of many stout plates, 



Family Scalpellid.e. 

 Genus MiteUa. 



6^ Peduncle nude Family Lepadid.«. 



c\ Capitulum covered by five large thin plates Genus Lepas. 



c^ Plates of the capitulum very small or wanting Genus Conchodcrma. 



Family BALANID.^. 

 Genus TETRACLITA Schumacher. 



Acorn barnacles composed of four compartments, externally cal- 

 cified together, obliterating the sutures in some species ; permeated by 

 pores in several rows; base flat, calcareous or membranous. 



The single Peruvian species is readily distinguished from Balanus 

 by the absence of external sutures and the thick spongy walls. 



TETRACLITA POROSA (Gmelin). 

 I'late IG, fig. 2. 



1791. Lcpas porosa Gmelin, Syst. Nat., 13th ed., p. 3212. 

 1854. TctracUta porosa Gmeliu, Darwin, Monograph on the Cirripedia, 

 BalauidiP, p. 320. 



Localihj. —Fayhx (Dr. W. H. Jones, U. S. Navy). 



The barnacle is rounded-oval in contour, conic, with a rather 

 small orifice. The sutures are obliterated externally, though visible 

 inside, and the outer layer of the Avall is removed in adult shells, 

 leaving the surface peculiarly tessellated by exposure of the ends 

 of the fiUed-up pores. The wall, viewed from the base, is seen to be 

 reduced to a spongy texture by the crowded pores. The usual size 

 is about 30 nun. long, 12 to 15 high. The opercular plates are tri- 

 angular, as in Balanus. 



Genus BALANUS Da Costa. 



Acorn barnacles with walls composed of six compartments, the 

 side areas or radii of the rostrum overlapping the alee of the adja- 

 cent lateral compartments; lateral compartments with ahv on the 

 rostral, radii on the carina! sides; walls permeated by usually only 

 one row of pores or none ; rostrum with ala^ only. Opercular plates 

 triangular, the scutum and tergum interlocking. 



Besides the following species, several others will probably, from 

 their known distribution, be found on the Peruvian coast." 



'^Balanus amphitrite niveus Darwin has been reported from "Peru on Venus 

 flex.'" by Weltner ; but Venus flexuosa is a species unknown on the west coast 

 of America, and no other locality on that coast has been recorded for the 

 barnacle in question. 



