CONCHOLOGY. 19 



C. testudinaria. The Tortoise Coronula. 



Very depressed, circular, as if radiated by the disposition 

 of marked spaces, striated transversely, forming six rays di- 

 verging from the centre to the circumference ; aperture oval 

 and hexagonal. 



C. halanarum. The Whale Coronula. 



A little more elevated ; the spaces prominent, equal be- 

 tween them, much larger than the excavated ; the aperture 

 subcircular ; the operculum of four valves, almost equal, oc- 

 cupying but a small space of the membranous part which 

 forms between them a sort of tube. 



C. diadema. The Crown Coronula. 



More elevated, sub-hexagonal ; the spaces almost equal, 

 the hollow parts larger than the saliant ; the superior aper- 

 ture very large and hexagonal ; the inferior much smaller, 

 of the same form, and communicating in a round excavation 

 by radiated plates ; the operculum bivalve. 



C quinquevalvis. The five-valved Coronula. PI. 4, 

 fig. 3. 



Species irregular, having only five valves, of a purple hue. 



3. Balanus. The Acorn Shell. Twenty-eight species. 

 So named from its resemblance to an acorn. Shell coni- 

 cal ; the coronary part formed of six very distinct valves, 

 one dorsal, one ventral, and two pairs of laterals, with or 

 without a calcareous support ; operculum of four articulated 

 pieces, forming a sort of pyramid in the superior aperture of 

 the tube. 



Balanus angulosus. Balanus palmatus. 



B. sulcatus. B. stalactiferus. 



B. tintinnabulum. B. plicatus. 



B. nigrescens. B. duploconus. 



B. cylindraceus. B. patellaris. 



B. calycularis. B. semiplicatus. 



B. roseus. B. galeatus. 



