THE SESSILE BARNACLES. 63 



Tergum rather narrow, with the spur normal in position, but rather 

 short; furrow nearly or quite closed; growth-ridges much more 

 prominent than in B. t. tintinnabulum; radial strise rather weak or 

 wanting. 



The cirri are generally similar to those of B. t. tintinnabulum, except 

 that the last three pairs have not nearly so many segments, with 

 compensating far greater length of the individual segments. There 

 are fewer distal spinules on the segments, but the same number (four) 

 of anterior pairs of spines. (See p. 52, fig. 8; p. 67, fig. lie.) 



The penis is as long as the posterior cirri. There are a few sparse 

 hairs near the end, but no basi-dorsal point was seen. 



A general view of the cirri and penis is given in figure 8. 



The opercular valves of this race are most like those of B. t. con- 

 cinnus, but the slight deflection of the tergal segment of the scutum 

 is a conspicuous differential character. The acute adductor ridge 

 and the conspicuously crimped growth ridges of the scutum serve 

 to separate the Terciera form from B. t. tintinnabulum. The rather 

 sharp, irregular ridges of the parietes and especially the smaller 

 number and mucli longer segments of the posterior cirri, are also unlike 

 that race. The color of the sheath is such as one often sees in tintin- 

 nabulum, and not darkened as in B. t. zebra, or specially colored, as 

 in some other races described by Darwin. 



The specimens were much overgrown with seaweed and incrusted 

 with lime. 



BALANUS TINTINNABULUM ANTILLENSIS, new sttbspecies. 

 Plate 13, figs. 1 to 2e. 



Type. No. 2083, A. N. S. P., St. Thomas, R. Swift. 



Distribution. West Indies to Rio Janeiro. 



The barnacle is small, somewhat tubular, with irregularly ribbed 

 parietes; white or whitish, with reddish purple lines on the parietes, 

 or the latter may be Indian lake throughout. Radii wide, whitish. 

 Insides of parietes dusky, sheath elsewhere pale. 



Diameter. 18 mm.; length 28 mm. 



Diameter 21 mm.; length 25 mm. 



Diameter 26 mm. ; length 33 mm. 



The opercular valves are formed substantially as in typical tintin- 

 nabulum; but the spur is somewhat shorter, twice its own width from 

 the basi-scutal angle; the terga are white or nearly so, and are about 

 as wide as the scuta. The adductor ridge of the scutum is better 

 developed, long and narrow, especially in the smaller examples. 



The type of this race is in a group (pi. 13, fig. le) which grew upon 

 an oyster shell. The largest measurement given above is from the 

 largest individual of the group, evidently an old one. A few Tctra- 

 clita radiata grew upon the same group. So far as I know, this is 



