100 BULLETIN 93;, UNITED STATES NATIONAL MUSEUM. 



The second cirrus has 23 and 16 segments, protuberant on both 

 rami. The anterior ramus is about 5 segments longer. 



The third cirrus has rami of 20 and 17 segments. The anterior 

 ramus has recurved teeth on the anterior side of the first nine seg- 

 ments, and there are some erect spinules near the anterior distal 

 angle on most of the segments. The posterior ramus has very few 

 straight teeth on a few of the lower segments (fig. 24&). 



Cirrus iv has no teeth or spinules on the segments. 



Cirrus vi ha,s five pairs of spines on the median segments, with a 

 few small spines springing between the large spines of the upper 

 four pairs (fig. 24c). Lowest pair is much smaller than the others. 

 The penis is about equal to the posterior cirri in length. 



I at fh'st described this form as a distinct species, but a larger 

 acquaintance with this group of Balanus induces me to reduce it to 

 subspecific rank, although it is as distinct from amphitriie as several 

 East Indian forms described as species. At present we know very 

 little about west American forms of the amiiliitrite group — only 

 what is contained in this work — and the final status of the several 

 forms existing from Lower California and Peru can not be foreseen. 



B. a. peruvianus is closely related to B. amphitritc, but it differs in 

 the following characters: (1) It is a much stronger barnacle, with the 

 parietal tubes filled up solidly, except close to the base. (2) The 

 basis clings strongly to the walls and has very few pores. (3) The 

 sheath is dark colored. (4) The tergum is flat outside, and has a 

 wider spm*. Finally, it reaches a larger size. 



The opercular valves are variegated with dark rays or areas, as 

 in dark forms of B. aiiipliiirUe. The moath parts and cirri do 

 not differ materially from those of B. ampJiitrite. The pores of the 

 parietos are filled up except close to the base, and might readily be 

 overlooked. The basis is not solid, as I stated in the original descrip- 

 tion. It has distinct pores, near the periphery only, which did not 

 appear in the sections I made at fii'st. They may be seen in plate 

 24, figm-e 4, which shows part of the basis adhering to the rostrum. 



BALAKUS CONCAVUS Bronn. 



Plate 21, figs. 1-lc. 



1831. Balmius conccmis Bronn, Italiens Tertiar Gebilde uud deren orgaiiische 



Einschliisse, p. 127- 

 1838. Balanus concavus Bronn, Lethsea Geognostica, vol. 2, p. 1155, pL 36, 



fig. 12a-e. 

 1854. Balanus concavus Bronn, Darwin, Monograph, p. 235, pi. 4, figs. 4a-e. 



Monograph on the Fossil Balanidte and Verrucidaj of Great Britain, p. 17, 



pi. 1, figs. 4a-p. 

 1904. Balanus concavus Bronn, G. 0. Martin, Maryland Geological Survey, 



Miocene, p. 94, pis. 33, 34 (=-B. c. chesapeaJcensis). 



