94 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



and first of all, the Darwin collection must be restudied and type 

 localities for his varieties selected. Large series from single colonies 

 must be dissected, in order to ascertain the constancy of the peculiar 

 features of the third cirri, which Darwin did not notico. After 

 working more than a week upon the American specimens, my impres- 

 sion is that the armature of the cirri varies a good deal; yet there 

 may possibly be more than one race in the Atlantic coast series I have 

 grouped under B. a. niveus, or two or three races may be mingled 

 in a hybrid population. In many lots the gray lines of the parietes 

 are faint, or they may persist only on the carina; sometimes they 

 can not be made out ; these variations occurring in the same colony. 

 In most of the northern and some southern examples the epidermis 

 persists over both parietes and radii, as in var. pallidus Darwin; and 

 these forms do not agree with Darwin's definition of his var. niveus; yet 

 to separate them from others of the same neighborhoods which are 

 nude when adult would be an arbitrary course. In most of the Flor- 

 ida colonies there are a few individuals with lavender or violaceous 

 tinted parietes, or with the lines lavender or plumbeus rather than 

 gray; but these colors do not appear in the lots from north of Dela- 

 ware. It may be noted that Darwin gives Florida among his localities 

 for variety niveus. 



A diameter of over 10 mm. is rare north of Hatteras. 



B. a. niveus is one of the most abundant barnacles where suitable 

 bottom is found, coating wood and especially shells in prodigious 

 numbers, as far north as Vineyard Sound. It does not go, appar- 

 ently, north of Cape Cod. The wide radii of these northern examples 

 differentiate them readily from the much rarer B. improvisus; but 

 externally they are not readily distinguishable from young B. eburneus. 



Sarasota Bay, Florida. Most specimens are white with gray lines 

 and white radii, but scattered among them are individuals of various 

 lavender tints, or with the lines lavender tinted, radii sometimes 

 pink. The colored individuals are connected with the white by 

 others of nicely graduated tints. The scuta are dark in some indi- 

 viduals, whether the walls are dark or light. Epidermis very thin 

 or wanting. Maximum diameter about 12 mm. 



Marco, Florida. A second set from this place has the labrum, 

 palpi, mandible, and posterior cirri as described above. The maxilla 

 has seven spines between the upper and lower pairs. The first cirrus 

 has 18 and 13 segments (fig. 20c). Cirrus ii, 15 and 13 segments, 

 rami subequal. Cirrus iii has 15 and 13 segments, the anterior 

 ramus about throe segments longer. The anterior ramus has 10 

 segments set with short, conic teeth, and some longer twin spines dis- 

 tally (fig. 20&). Posterior ramus with nine armed segments (fig. 20a). 



Pine Key, Florida. Similar to the Marco lots and intermediate 

 between them. The labrum has two and three teeth on the two sides. 



