SESSILIA. 151 



large, slightly united, having an orbicular plate concave inter- 

 nally at the base. 



^cas/a Jllonto^m'.— Montagu's AcASTA. Plate XIX. fig. 

 8, 9. Valves erect, triangular, acute, with muricated ascending 

 spines. Inhabits the British seas. 



Genus 4. — ADNA.— Z-eac^. 



Generic Character. — Cup-shaped, sessile, shell composed of 

 one part ; aperture lozenge-shaped ; with four valves. 



Adna Anglica. — The English Adna. Plate XIX. fig. 28. 

 Shell and base externally, and slightly ribbed ; of a fine rose 

 colour ; operculum transversely striated. Inhabits the Devon- 

 shire coast, attached to the Coryophyllia Anglica. 



Genus 5. — B ALAN US Bruguiere. 



Generic Character. — Body sessile, inclosed in an operculated 

 shell ; branchiae numerous, placed in two rows, unequal, articu- 

 lated, ciliated ; each composed of two cirri, supported by a pe- 

 duncle, and exsertile ; mouth with four transverse and dentated 

 jaws, and provided with four hairy palpi-like appendages.— Shell 

 sessile, conical, composed of four valves, locked together, closed 

 at the base by a testaceous plate ; aperture subtrigonal or ellip- 

 tical ; operculum internal, and consisting of four moveable valves. 



Balanus candidus. — The White Balanus. Plate XIX. 

 fig. 10. and 11. White; valves nearly smooth; operculum 

 strongly ridged transversely, wath longitudinal, nearly obsolete 

 striae. Two inches broad at the base. Inhabits the Frith of 

 Forth. 



Genus 6 CORONULA. —Zamarc^. 



Generic Character. — Body seated, enveloped in a shell, vi-ith 

 small setaceous and cirrous arms. — Shell sessile, suborbicular ; 

 valves apparent, indivisible, conoid, or conically truncated at the 

 extrem.ities, with very thick walls, and interiorly hollowed in 

 radiating cells eighteen in number ; aperture regular, of a rounded 

 oval, and interiorly funnel-shaped ; operculum having four ob- 

 tuse valves. 



