186 BULLETIN" 93, UNITED STATES NATIONAL MUSEUM. 



Labrador specimens seen are rather small, all of the patelliform 

 shape, and like those of New England. 



In New England B. balanoides is an exceedingly abundant bar- 

 nacle, on rocks between tides, on piles and buoys, and on the mussels 

 growing there ; in such places they often become larger than those on 

 shore rocks in the same vicinity. 



The low-conic form may be either sharply, strongly ribbed, as in 

 plate 44, figure 5, from New Haven, Connecticut, on Mytilus edulis, 

 or it may be moderately folded as in plate 44, figure 2, on bark of a 

 pile, New Haven, Connecticut. The less-ribbed form is the common- 

 est and closely resembles European specimens. When they stand 

 crowded the walls become subvertical and higher than the conic form, 

 yet often with no tendency toward the tubular form. Another lot 

 from the same locality, growing on oyster shells, vary from shortly 

 cylindric to hourglass shaped. 



The tubular form, growing in crowded masses (pi. 44, figs. 2, 

 7-7^7, Savin Eock, New Haven, Connecticut), is excessively variable 

 in shape. The individuals cohere rather weakly, and may usually be 

 separated without breaking. The compartments are often calcified 

 together in the lower part. Parietal tubes square, the septa thin, but 

 usually they are closed at the basal edge. Two very slender indi- 

 viduals measure : 



Length 46 mm. ; greatest diameter 8.3 mm. ; least 3.3 mm. 



Length 2G mm. ; greatest diameter 4 mm. ; least 1.5 mm. 



In the Savin Rock colony the tergum is slightly narrower than 

 usual, but it is identical in shape in the patelliform and the tubular 

 (pi. 44, fig. 6) forms. I have noted above that the mouth parts and 

 cirri are practically identical in patelliform and tubular individuals. 

 In some groups one may trace all transitions of contour from the 

 low-conic to the tubular. 



Plate 45, figures 2, 2, represent tergum and scutum of a small, 

 deeply corroded form of balanoides, growing in the vicinity of the 

 following form. 



Variety with a narrow spur and numerous spines on the later 

 cirri. This form, figured on plate 45, figures 1 to !<?, has been 

 noticed by Darwin as var. a. I have seen it from Nahant, Massa- 

 chusetts, collected by Prof. A. S. Pearse. It is somewhat conic with 

 rather large orifice, weak, the walls smooth, thin, compartments 

 readily separable, the parietes having regular square tubes not oblit- 

 erated at the base, and separated by thin septa, but the interior is not 

 ribbed. The scutum does not differ from that of normal B. bala- 

 noides, but the tergum (pi. 45, fig. 1, Ic) has the spur narrow, longer, 

 and pointed, unlike the ordinary form in B. balanoides. The seg- 

 ments of the posterior cirri have seven pairs of spines (p. 190, fig. 



