280 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



The}^ are finely striate vertically and crenulated at the basal edges. 

 In 3'oiing specimens the ribs are simple, but in old ones they branch 

 more or less freely, most of the branches not reaching to the periph- 

 ery. Normally there are 30 ribs and 30 lobes of the basal margin of 

 the body-chamber. Earely an individual ma}^ have one or more com- 

 partments with only three or four loops of the inner wall, with 

 branches parallel with and close to the upper side, so that an in- 

 complete outer wall, analogous to that of Coronula^ is formed. 



In section it is seen that the inner wall is very dense and solid, but 

 has a friable outer layer, which is closely porous, and which forms 

 the greater part of the substance of the ribs. 



The radii are as thick as the compartments and their edges are 

 intricately sculptured with crimped sutural laminas (pi. 0(3, figs. 

 6, 5(2). The sheath is transversely grooved, a little shorter than the 

 body-chamber, and its lower margin is not overhanging or prominent. 



The scuta are juxtaposed as in Coronula. Their upper layers 

 scale off. Terga very small. 



" Color of membranes, when living, sulphur yellow ; hood extremely 

 protrusile." 



It is excessively variable in size, proportion of diameter to height, 

 and shape of the ribs or lamella3, which may be short, with a rounded 

 (semicircular) outline, or long, and triangular in outline. The ribs 

 may have many or very few branches. Apparently adult individuals 

 measure as follows : 



Greatest diameter, 55 mm. ; height, 15 mm. 



Greatest diameter, 49 mm. ; height, 16 mm. 



Greatest diameter, 37 mm. ; height, 18 mm. 



In young specimens the shape is that of a thick disk with rounded 

 periphery, and the folds are simple. At all stages their free edges 

 are beautifully crenulated. 



Plate 66, figure 3 represents the usual appearance in the skin of 

 the whale, the hood contracted. In figures 2, 2a the lateral com- 

 partment of a cylindric individual, with very short parietal ribs, 

 is drawn. The usual forms have the wall triangular (fig. 5) or 

 irregularly convex (fig. 5«.) in section. Figui'es 1, 3, 4 are top views, 

 1«, 4<z basal views. 



The porous, friable texture of the radial lamella? make this bar- 

 nacle extremely hard to disengage from the skin of the whale. Prob- 

 ably the best w^ay would be to macerate fresh specimens, or have 

 them cleaned by ants or Dermestes. After being in alcohol the whale 

 skin becomes extremely hard and tough, and treatment with caustic 

 soda loosens part of the lamellae, besides separating the compartments. 



Upon the opercular membrane, and especially in the shallow cavi- 

 ties of the eroded radii, one often finds the little parasite Cyamus 

 clinging. 



