THE SESSILE BARNACLES. 



87 



and they may be known by the more unequal rami of the first cirri, 

 the armature of the third cirri, and the teeth of the labrum, which 

 do not form a long, regularly graduated series, as is usual in B. 

 improvisus. The spur of the tergum of B. improvisus is longer and 

 narrower than that of B. amphitrite niveus, and it has the external 

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

 differs from improvisus by wanting a distinct adductor ridge in the 

 scutum, among various 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 IMPROVISUS, WDIYAH BAY, SOUTH CAROLINA, a, b, LABRUM. c, MEDIAN SEGMENT 



OF CIKRUS VI. d, PALPUS. C, MAXILLA. /, OUTER FACE OF A SEGMENT OF CIERUS III. O AND / ARE FROM 

 ONE INDIVIDUAL, b- FROM ANOTHER. 



In a specimen from Quinnipiac River, Massachusetts, the first 

 cirri have equal ranii. 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 teeth, such as B. amphitrite has. The sixth 

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

 has about 16 teeth on each side. 



Specimens from Fisli HawJc stations 1641-2, Winyah Bay, South 

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

 5 to 7 mm. high, with subverticai walls and large 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. 



