AcTiNEA. RADIATA. ACALEPHA. 497 



ACALEPHA. 



I. Sect. — Fixed ; the base, opposite the mouth, adhering to 

 other bodies. 



A. Tentacula surrounding uninterruptedly the oral disc. 



Actinea. 

 Mammaria. 



A A. Tentacula on the margin of the oral disc disposed in tufts. 

 Lucernaria. 



II. Sect. — Free ; the base opposite the mouth incapable of ad- 

 hering to other bodies. 



A. Body closed opposite the mouth. 



a. Body strengthened internally by a cartilaginous plate. 

 Velella. 



aa. Body destitute of an internal cartilaginous plate. 

 b. A mouth in the centre of the oral disc, 

 c. Destitute of lateral cavities. 

 Eulimena. 

 Geryonia. 

 cc. With four lateral cavities, or ovaries. 

 Cyanea. 

 bb. Destitute of a mouth in the centre. 

 Rhizostoma. 

 Cassiopea. 



AA. Body open at both extremities. 



Beroe. 

 Pleurobrachia. 



Gen. XVI. ACTINEA.— Base Avith the disc capable of shift- 

 ing place ; mouth terminal, retractile ; tentacula numerous. 



41. A. equina. — Body smooth, finely wrinkled transversely; 

 margin of the disc with a row of tubercles. 



A. equina, Linn. Syst. i. 1088 — Hydra disciflora, tentaculis retractilibus, 

 extimo disci margine tuberculato. Gaertner^ Phil. Trans* 1761i t. i. 

 f. 5. Dicqemare, PhU. Trans. 1773, 3G4. t. xvi. f. 1 — A. hemisphserica, 

 Penn.'Brit. Zool iv. 50. — A. mesembryantljemum, Turt. Brit. Fauna, 

 131. — A. rufa, StewarVs El. i. 303 — Common, adhering to rocks. 



Body, when contracted, hemispherical, red or brown, smooth ; base black- 

 ish-grey, with unequal, tubercular, diverging ridges, the margin with a pur- 

 ple ring; tentacula numerous, lengthened, of the colour of the body, or va- 

 riegated ; exterior to which, there is a ring of about twenty purple tubercles ; 

 the margin of the mouth is slightly tinged with purple. 



VOL. I. I i 



