362 MALENTOZOA. SESSILIA. 



strong. When on shells, it corrodes a cavity into their 

 suhstance. 



Abundant on rocks, and frequently on limpets and mussels. 



Although named punctatus hy Montagu, the puncturation of 

 the coronary tube and operculum is not essential to it ; and 

 an Indian species being so named by Chemnitz, we must take 

 Pennant's name. 



Balanus punctatus. Mont. Test. Brit. 8. PL 1. f. 5. Balanus 

 punctatus. Brown, Illustr. PL vii. f. 13. Lepas Cornubiensis, 

 Penn. Brit Zool. iv, PL 40. f. 3. 



3. Balanus communis. Common Acorn-Shell. 



Shell conical, truncate, with the six valves often indistinct, 

 longitudinally sulcate, with prominent, compressed, obtuse, 

 rugose ridges, rendering the base very angular ; the interstices 

 transversely striate; the aperture ovate, subpentagonal, mo- 

 derate ; the ventral opercular valves triangular, acute, with 

 strong transverse rugae ; the dorsal narrow, triangular, acumi- 

 nate, considerably curved, much longer than the others, simi- 

 larly striato-rugose, with finer striae toward the end, a wide 

 longitudinal groove on each side, and a dorsal keel ; the base 

 calcareous ; the colour white, tinged with yellow or grey. 



It occurs on rocks, shells, Crustacea, algae, and other ob- 

 jects, often on Fusus antiquus, Buccinum un datum, and other 

 shells, from deep water, but also along the shores. When 

 crowded, it is often considerably modified, but is always easily 

 distinguishable. It is very strong, and adheres more firmly 

 than any other species. 



Lepas Balanus. Linn. Syst. Nat. 1107. Balanus communis. 

 Mont. Test. Brit. 6. Lepas Balanus. Nat. and Rach. Linn. Tr. 

 viii. 23. Balanus sulcatus. Lamk. Syst. v. 390; Ed. 2. v. 657. 

 Balanus communis. Brown, Illustr. PL 6. f. 1, 13. 



4. Balanus costdtus. Ribbed Acorn-Shell. 



Shell conical, truncate, with the six valves united, longitu- 

 dinally marked with straight, prominent, compressed, convex, 

 strong ribs, running out upon the base, and rendering it an- 

 gular ; the surface also concentrically striulate ; the aperture 

 small, ovato-pentagonal; the ventral opercular valves trian- 

 gular, acute, with transverse rugae ; the dorsal narrow, trian- 

 gular, striated ; the base calcareous ; the colour white. 

 Diameter from half an inch to an inch. 



On shells from off Aberdeen; not common. 



