THE SESSILE BARNACLES. 71 



Tergum whitish, striate on the carinal area, with growth-ridges on 

 the scutal area; furrow closed or almost closed; spur narrow, fully 

 double its own width, or more, from the basiscutal angle. 



This form differs from B. t. concinnus of the mainland by the flat 

 scutum. I have compared scuta of concinnus of the same size and 

 smaller, and in all of them the tergal segment is broadly deflected, as 

 in the adult stage. The external color reminds one of B. concavus. 



B. t. coccopoma also has a wide deflected tergal border of the 

 scutum, and the external form and color are different. 



In specimens of B. t. tintinnabulum a little larger than the Gala- 

 pagos form, the tergal edge of the scutum is noticeably -inflected. 

 Otherwise there seems little difference between them. Possibly the 

 Galapagos specimens may be the descendants of imported examples of 

 this oriental subspecies, though it seems to me rather unlikely? Dar- 

 win mentions tintinnabulum from the Galapagos, without comment. 

 As- he treats rather fully of the West American forms, it would seem 

 likely that if he found "var. communis 3 ' there he would have made 

 note of it. 



Over 60 individuals are grouped on a volcanic rock about 8 inches 

 long. From the nearly equal size of the larger ones, of the bases 

 left by their departed brethren, and the nearly closed furrow of the 

 tergum, it may be inferred that they are nearly or quite adult; yet I 

 feel some doubt on account of the fact that the parietes below the 

 sheath are ribbed. In the fully adult stage, B. tintinnabulum has a 

 smoother interior. Some individuals of the smaller subspecies, such 

 as occator and spinosus I have examined are strongly ribbed within, 

 though doubtless of full size; others, probably older, though not 

 larger, have the interior smooth, except near the base. However 

 this may be, it appears that the Galapagos form differs from other 

 known races of the west coast of the Americas and should be readily 

 recognizable, even if it proves to attain a size greater than the 

 type lot. 



There is another West American form of tintinnabulum apparently 

 differing from those described above. It was taken by Dr. L. Plate 

 at Cavanche, near Iquique, to a depth of 50 meters, and has been 

 described by Weltner. 1 The shell is white, and rather strongly 

 ribbed, "like porcatus" the sheath uncolored or pale rose; radii are 

 very oblique. The scutum has sculpture like occator. The size is 

 up to 30 mm. in height. In color it cartainly resemblos B. psittacus. 



Other named oriental forms of B. tintinnabulum may be men- 

 tioned here. Variety intermedius Darwin, locality unknown, and 

 var. dorlignyii Chenu, which Darwin reports from a ship from 

 Java, are not represented in the United Statss National Museum 

 collection. 



1 Archiv fur Naturgeschichte, 61 Jakrg., 1895, p. 291. 



