74 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



The penis is more than twice as long as the last cirri, and has a 

 conspicuous, acute, basidorsal point. 



Several hundred specimens in the United States National Museum 

 show this to be a distinct species of the tintinnabulum group. They 

 have the form and appearance of mature barnacles. Nearly all of 

 those I opened contained large masses of eggs, of the usual elliptical 

 shape, and from 0.12 to 0.14 mm. long, much smaller than the eggs of 

 tintinnabulum. While we know that Balanus reproduces long before 

 attaining its maximum size, yet the eggs produced by small individuals 

 equal in size those of the larger. The great number of spines on the 

 later cirri is also a feature of maturity. Very young barnacles have 

 fewer spines than old ones. I am therefore convinced that these 

 pygmy barnacles are mature. I believe that Darwin had the same 

 race before him, but mistook it for young B. tintinnabulum, when he 

 stated that ' ' in some young specimens from the Cape of Good Hope 

 * * * I found six pairs of spines on the segments of the posterior 

 cirri." (Monograph, p. 200.) 



While this barnacle is certainly related to B. tintinnabulum by the 

 shape of the terga, it differs in so many characters that I can not 

 rank it as a subspecies. Except the small size, these characters are 

 not directly correlated with its peculiar station. The structure of the 

 walls is that common to species of Megabalanus, but special differen- 

 tial features of B. algicola are: The small size and pale color; simpli- 

 fied sutural septa (those of B. tintinnabulum being denticulate on 

 both sides); the broad scuta; the short lower teeth of the mandible; 

 the numerous spines of the posterior cirri, and the absence of spinules 

 along the distal borders of the segments. 



B. algicola grows on alga?, usually in masses mounted upon one 

 another, and is apparently a very abundant form. 



BALANUS AJAX Darwin. 



1854. Balanus ajax DARWIN, Monograph, etc., p. 214, pi. 3, figs, la-lc?. (Philip- 

 pine Archipelago.) 



1884. Balanus ajax Darwin, FISCHER, Bull. Soc. Zool. de France, vol. 9, p. 357. 

 1907. Balanus ajax Darwin, GRUVEL, Bull. Soc. Zool. de France, vol. 32, p. 164. 



Locality. Mariveles, Luzon, Paul Bartsch. Cat. No. 43498, 

 U.S.N.M. 



I do not find that any definite locality in the Philippines has been 

 given for this barnacle, which, though related to B. tintinnabulum, is 

 characterized by its "excessively strong, massive, and heavy" walls, 

 dark sheath, and large rostral compartment. According to Dr. Paul 

 Fischer, it has been collected by Lambert from reefs south of the 

 Isle of Pines, New Caledonia. Professor Gruvel adds the localities 

 Salomon Island, in the Chagos Archipelago, and Seychelles. 



