ECTOPLEURA. 423 



Agassiz has shown that tlie gcnciMl orange colour of the stem is produced by longitudinal 

 bands of pigment cells upon the inner wall of the coenosarcal cavity. He has further shown 

 that this wall forms ridges which project into the cavity of the stem, but that the cavity itself, 

 unlike that of Tuhularia indivisa, is single and continuous, while its walls, except on the bands 

 of pigment cells, are clothed with vibratile cilia. 



ECTOPLEURA, Agassis. 



Name. — From kruc, on tlie outer side, and irXivpa, a rib, in allusion to the prominent 

 longitudinal ribs of the planoblast. 



TuBULAUiA, — Van Beneden. 



TROPHOSOME.— Hydrocaulus filiform, rooted. Htdeanths flask-shaped, 

 abruptly marked off from the supporting stalk ; tentacles of the proximal set longer 

 than those of the distal. 



GONOSOME. — Planoblasts on branched peduncles, which are borne on the body 

 of the hydrantli between the proximal and distal verticils of tentacles. Medusa at 

 the time of liberation with a nearly spherical umbrella and simple-mouthed manu- 

 brium ; four radiating canals and four marginal tentacles ; no distinct ocelli ; umbrella 

 furnished with eight prominent longitudinal ribs, formed of linear series of thread- 

 cells. 



To his genus Edopleitra, Agassiz, as has been already said, refers the Tuhularia Dumortieri 

 of Van Beneden. In thus separating Van Beneden's Tuhdarian from the true Tulularm, 

 Agassiz seems to me to be fidly justified, the phanerocodonic condition of the gonophore 

 affording in itself an- important generic character. I cannot, however, so easily assent to the 

 correctness of associating with it in the same genus the Sarsia pulcheUa of Forbes, the Sarsia 

 turricula of M'Crady, and the Sarsia nodosa of Busch.^ These hydroid medusae are very 

 different from the medusa of Van Beneden's Tuhularia Dumortieri, while one of them, Sarsia 

 turricula, has been traced by M'Crady, if not with absolute certainty, at least with high proba- 

 bility, to a coryniform trophosome." 



It is possible that the medusa named Ectopleura ocracea by Mr. A. Agassiz,' has been 

 rio-htly referred to this genus ; but as we know nothing of its trophosome, its generic determi- 

 nation cannot be regarded as otherwise than provisional. 



' See Agassiz in ' Cont. Nat. Hist. U. S.,' vol. iv, p. 343. 

 - ^I'Crady, in ' Gyiiophth. of Charleston Harbour.' 

 » ' Illustr. Catal./ p. 191, fig. 320. 



