testaceous plate. The opening on the top closed by four 

 moveable valves, inserted near the base of the inside of 

 the shell. 



* B. COMMUNIS. Lepas Bilanus. Turt. Lin. L. Cor- 

 nubiensis. Pen. Brit. Zo., vol. 4, pi. 37, fig. 6. B. C. 

 Mont. Test. Brit., vol. 1, p. 66. Stew. Elem., vol. p. 363. 

 Acorn shell. Common on rocks ; clustering. 



* B. BALANOIDES. Lepas B. Tnrt. Lin. Pen. Brit, 



Zo., vol. 4, pi. 37, fig. 5. Stew. Elem., vol. 2, p. 364, 

 B. B. Mont. Test. Brit., vol. 1, p. 7. Covering rocks, 

 in multitudes. 



* B. PUNCTATUS. Mont. Test. Brit., vol. 1, p. 8, and 

 pi. 1, fig. 5. This has generally been confounded with the 

 preceding: a circumstance not surprizing, from the little 

 attention hitherto paid to these animals, and the difference 

 of their form from variety of position, clustering and age. 



B. TINTINNABULUM. Mont. Test. Brit., vol. l, p. 10. 

 Montagu describes this shell from specimens attached to 

 the bottoms of ships from warm climates ^ but doubts of its 

 being a native of our seas. I have found numerous speci- 

 mens, answering to his description in all but size, attached to 

 the surface of the Nidus of Buccinum Undatum, thrown on 

 shore on the beach, and consequently from no great distance 

 in the ocean. A comparison of these specimens, scarcely a 

 line in diameter, with the foreign shells, which are among 

 the largest of the genus, mav lead to a suspicion that they 

 are not certainly identical ; in which case the Cornish will be 

 a new species ; but this must be left for further investigation. 

 The colour of this shell is pure white ; of the inner valves 

 purple. 



ACASTA 

 GENERIC CHARACTER: The shell sessile, oval, sub- 

 conic; formed of separable pieces, forming six unequal 

 plates; the bottom a convex plate externally. Cover with 

 four valves. 

 A. MONTAGUI. Crouch's Introduction to Lamark's 

 Conchology, pi. 1, fig. 15. This species does not fix on 

 solid bodies, but lives embedded in sponge. It is obtained 

 from deep water, and is scarcely common. 

 CREUSIA. 

 GENERIC CHARACTER: The shell sessile, fixed, or- 

 bicular, with four plates, which are unequal, united by 

 distinct sutures. Cover internal, with four valves. 



* C. STRIATA. Lepas Intertexta. Turt. Lin. L. Striata. 

 Pen. Brit. Zo., vol. 4, pi. 38, fig. 7. Balanus S. Mont. 

 Test. Brit., vol. 1 p. 12. L. S. Stew. Elem., vol. 2, 

 p. 364. Common on shells, rocks, and the stalks of sea- 

 weeds where not often uncovered by the tide : clustering, 

 but not so as to influence the regularity of growth. 



