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. 



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

 Lucernaria. 



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

 hering to other bodies. 



A. Body closed opposite the mouth. 



a. Bodv 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. 

 Ithizostoma. 

 Cassiopea. 



AA. Body open at both extwnities. 



Beroe. 



Pleurobrachia. 



Gen. XVI. ACTINEA.— Base with 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. 1761, t. i. 

 f. 5. Dicqemare, Phil. Trans. 1773, 364. t. xvi. f. 1— A. hemisphaerica, 

 Penn. Brit. Zool iv. 50. — A. mesembryanthemum, Turt. Brit. Fauna, 

 131.— A. rufa, Steivarfs El. i. 393 — 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 



