THE SESSILE BARNACLES. 



87 



and they may be known by the more uncqiuil rami of the first cuti, 

 the armature of the third cirri, and the teeth of t]ie hibrum, which 

 do not form a long, regidarly gi-aduated series, as is usual in B. 

 improvi^us. The spur of the tergum of B. imjjrovisus is longer and 

 narrower than that of B. amj^Mtrite niveus, and it has the external 

 furrow more developed, or at least distinctly indicated. B. crenatus 

 differe from impromsus by wanting a distinct adductor ridge in the 

 scutum, among vai'ious other differences. There are many lots of 

 improvisus and related species which can be determined only by a 

 deliberate examination of the whole animal. 



Fig. 17.— Balanus IMPRO\^sus, Wintah Bat, South Carolina, a, b, labkum. c, median segment 



OF CIRKUS Yl. d, PALPUS, e, MAXIU.A. /, OUTER FACE OF A SEGMENT OF CIRRUS lU. a AND / ARE FROM 

 ONE INDIVIDUAL, b-C FROM ANOTHER. 



In a specimen from Quinnipiac River, Massachusetts, the first 

 cirri have equal rami. Second cirri with subequal rami of 13 and 

 12 segments. Third cirri with rami of 15 and 12 segments, the 

 longer projecting four segments beyond the shorter; sides of the 

 segments spinose, without teetJi, such as B. ampliitrite has. The sixth 

 cii-ri have five pairs of spines on the segments (fig. 17c.) The labrum 

 has about 16 teeth on each side. 



Specimens from Fish Hawk stations 1641-2, Winyah Bay, South 

 CaroUna, are small, though adult, the largest about 5 mm. in diameter, 

 5 to 7 mm. high, with subvertical walls and largo orifice. Some of 

 them show white lines, and in the upper two-thirds the transverse 

 septa also show through. They grew on Mytilus exustus and on one 

 another, and some show the sculpture of the shell. 



