648 DESCRIPTION OF PLATES, 14, 15. 



c, outer lamina of wall of compartment. 



d, the exterior septum, connecting the outer lamina of the 



wall to the inner lamina ; the basal edge of the inner 

 lamina of the wall is seen beneath and without the lower 

 end of the inner portion (a) of the radius. 



PLATE 15. 



Genera — Chelonobia and Coronula. 



Fig. 1, Transverse section of shell of Chelonobia testudinaria. 



bab, Compound rostrum : a being the true rostrum. 



B B, the rostro-lateral compartments, which normally, in the 

 Balaninae, are quite confounded with the true rostrum : 

 the sutures separating these three compartments are not 

 continued through the outer lamina. 



c, left-hand lateral compartment. 



D, left-hand carino-lateral compartment. 



e, carina. 



s s, Sutures, six in number, separating the six compartments. 



a, outer lamina of wall of compartment, whence the radiating, 

 longitudinal septa (left unshaded) arise, and at the oppo- 

 site end blend into the indistinct inner lamina, viz. b, (see 

 fig. 4, in last plate.) 



c', sheath. 



d, ala, forming, as usual, part of the sheath. 



e, inner portion of the radius. 



f,f, outer lamina of the radius (see b, in fig. 5, in last plate), of 

 great thickness, and externally deeply pitted ; — the sharp 

 ridges between the pits, produce in the section the points, 

 such as that marked by the outer/*. 



2, Coronula balsenaris, shell seen from above. 



2 a, „ ,, section of one of the transverse circumferen- 



tial loops, formed by the folded wall 

 of a compartment. The wall itself is 

 formed of an outer and inner lamina, 

 with longitudinal septa. The internal 

 surfaces of the loop-part are connected 

 by special shelly plates or longitudinal 

 septa. 

 2 b, ,, ,, scutum and tergum united together by 



the opercular membrane (with horny ridges), seen from 



the inner side. 



3, Coronula diadema, shell, seen from the outside ; 3 a, scutum 



and tergum joined together by the opercular membrane, 

 seen from the outside ; 3 b, scutum cleaned and enlarged, 

 seen from the inside. 



4, Section, in a vertical plane, through the skin of a whale, on 



which a Coronula diadema had been attached, but has been 

 wholly removed : the two curved, horn-like projections 

 occupied two of the eighteen cavities on the under 



