THE SESSILE BARNACLES. 



331 



wall, its lower margin not in the least overhanging. The interior is 

 not in the least grooved below the sheath, and at the basal edge tho 

 compartments are very narrowly inflexed or have a slight rim around 

 the membranous basis. 



The carina is longer than the rostrum, longer than wide, triangular 

 in outline. The carinolateral compartments have very narrow, band- 

 like parietes, hardly one-fourth as wide as that of the rostrum. The 

 rostrum is normally about as high as wide, and triangular in shape. 

 The base is modified in shape by the cylindrical coral, which serves 

 as support, and upon which the barnacle is seated with the carino- 



u^ 



FIG. 98. HEXKLASMA AMERICANUM. a, INTERMEDIATE SEGMENTS OF ciuuus vi. 6, FIRST 



CIRUUS. C, MANDIBLE. d, MAXILLA. 



rostral axis transverse to the long axis of the coral-branch in all 

 but one of the specimens seen. 



Greatest carinorostral diameter, 17 mm.; basal diameter at right 

 angles to preceding, 18 mm. ; height of carina, 21 mm. 



The scutum is at least two and one-half times as long as wide, 

 sculptured with regular growth-ridges, which unite by pairs to form 

 oblique teeth along the occludent edge. There are no longitudinal 

 strise. Inside there is a very low, rounded, rather massive articular 

 ridge, and a deep, very narrow articular furrow, but no adductor 

 ridge whatever. There is a small pit with a couple of short crests 

 for the lateral depressor muscle. The occludent border of the plate 

 is bent up along its lower half. 



