THE SESSILE BAENACLES. 123 



Tliis barnacle is known to me only by specimens growing in crowded 

 groups, about 32 mm. long, about 11 mm. in diameter. Three- 

 fourths or more of the length is formed by the elongated basis. About 

 two-thirds of the total length is occupied by an openly cellular mass 

 formed of thin, irregular calcareous septa, variously anastamosing 

 and connected with those below and above, often having slender, 

 depending styles, which are frequently superposed in successive septa. 



This structure, although confined to this Cirripede, is not so anomalous as might at 

 first be thought, for in most species of the genus, each time that the circumference 

 of the basis is added to, an excessively thin calcified film is thrown down over its whole 

 inner surface; and in any of these species, if the films had been formed thicker and 

 had rested only on certain points, instead of over the whole underlying layer, the 

 cancellated structure above described would have been produced. (Darwin.) 



That part of the basis forming the side walls has a single series of 

 large, circular pores and an outer layer of small, irregularly placed 

 pores, resembling the parietal pores of Balanus cariosus, but of course 

 homologous with the vesicular, underlying layer of the basis found in 

 many species of Balanus. 



The peculiar cellular filling of the base is unique among recent bar- 

 nacles, but it is exactly similar to that of the fossil Tamiosoma gregaria 

 Conrad. 



Darwin found the scutum to have two furrows, tergum as usual. 

 Opercular valves are wanting in the specimens I have examined. 



This subspecies is not contained in the United States National 

 Museum. The specimen figured is No. 2056 A. N. S. P. 



BALANUS PERFORATUS Bruguiere. 



1789. Balanus perjoratus BRUGUIERE, Encyclopedia Me"thodique, p. 167 (Medi- 

 terranean coast of Barbary; Senegal). 



1854. Balanus perforatus Bruguiere, DARWIN, Monograph, p. 231, with varieties 

 angustus Gmelin, cranchii Leach, fistulosus Poli, and mirabilis Darwin. 



The localities given below practically cover the known range of 

 the species, as the localities West Indies and South America are men- 

 tioned by Darwin with doubt, and have not been confirmed. Darwin 

 considers it nearest to B. Isevis, which it often resembles closely in 

 outward form. The scuta, however, have plain, rather fine growth- 

 ridges, and no longitudinal furrows or striae. The cirri show a close 

 relationship to B. trigonus, but differ in some details, especially in 

 having the fourth to sixth cirri more fully armed with teeth along 

 the posterior margins of the proximal segments, as shown in. figure 32c. 



The armature of the cirri has not been described. Cirrus i has 

 very unequal rami of 30 and 14 segments, the posterior not much 

 more than half as long as the anterior ramus and with very long 

 appendages on the segments. 



Cirrus ii is about as in B. concavus, with equal rami of about 13 very 

 protuberant segments. 



