THE SESSILE BARNACLES. 43 



differences which we can only consider specific in the present state 

 of oni' knowledge. In the movable scutum of V. bicornuta the second 

 articular rib, parallel to the third or crescentric rib, is wider in V. rath- 

 buniana, and the median articular ridge of the movable tergum, 

 distinct in F. bicornuta, is represented by a low wave only. The 

 carina and rostrum interlock by more numerous, smaller teeth in 

 F. bicornuta. This is a conspicuous difference. The sculpture of 

 the fixed scutum and tergum of F. rathbuniana is extremely regular, 

 while in F. bicornuta it is uneven and irregular. The difference in 

 total contour is doubtless due to the accident of station, and the 

 same circumstance may possibly have affected the sculpture. The 

 nature of the support is unknown, since both barnacles had been 

 removed from their supports. F. rathbuniana evidently sat upon a 

 level surface, while F. bicornuta perched upon a small, irregular 

 prominence not admitting of free expansion of the base. 



Verruca, rathbuniana is one of the largest and finest of the erect 

 forms. It is named for Miss Mary J. Rathbun, of the United States 

 National Museum. 



VERRUCA BICORNUTA, new species. 



Plate 7, figs. 1-lc; plates 8, figs. 3-36. 



Type.Ca.t. No. 11027, U.S.N.M. 



Type-locality. Albatross station 2575, east of Nantucket, latitude 

 41 07' north; longitude 65 26' 30" west, in 1,710 fathoms, gray 

 ooze; bottom temperature 37 F. 



The barnacle is cream-white, high, with steeply sloping movable 

 plates; laterally compressed. Plates of the wall are not thick and 

 have a narrow hemlike ledge around the base. The apices of rostrum 

 and carina are produced beyond the outlines of the wall, forming short 

 horns. 



The movable scutum is thick. There are two contiguous narrow, 

 curved, beaded, articular ribs, the lower one reaching the basi- 

 tergal angle and defining a lunate, sloping tergal area. The tergal 

 edge protrudes weakly near the apex. When the scutum is isolated 

 there is seen to be a deep, narrow, articular furrow below the apex, 

 but this is not visible in complete individuals. The occludent area 

 of the plate has regular, strong, flat, imbricating ribs. The interior 

 face is deeply concave between the articular and outer raised borders 

 (fig. Ic). 



The movable tergum is rather thin, divided by a strongly raised 

 diagonal ridge, above which there are two articular ridges, the median 

 one low, wide near the diagonal, the other one stronger, a concavity 

 below it. The area below the diagonal has rib sculpture, like the 

 corresponding area of the scutum. The internal face is slightly con- 

 cave. The suture between scutum and tergum is nearly straight 



