368 Prof. AUman on the Comtruction and 



2. EcTOPLEURA, Agassiz. 



Trophosome. — Coenosarc invested by a chitinous periderm, 

 and consisting of a simple or branched hydrocaulus springing 

 from a filiform (?) hydrorhiza. Polypites flask-shaped, with 

 filiform tentacula arranged in two verticils, the proximal verticil 

 composed of tentacles which are longer than those forming the 

 distal verticil. 



Gonosome. — Gonophores phauerocodonic, on branched pedun- 

 cles, which are borne upon the body of the polypite, between the 

 proximal and distal verticils of tentacles. Medusa, at the time of 

 liberation, with a nearly spherical umbrella; a manubrium with a 

 simple mouth, and shorter than the height of the umbrella- 

 cavity ; four radiating canals, and four marginal tentacles ; no 

 distinct ocelli; the umbrella furnished with eight prominent 

 longitudinal ribs formed of linear series of thread- cells. 



To his genus Eetopleura Agassiz, as has been already said, refers 

 the Tubularia Dumortieri of Van Beneden. In thus separating 

 Van Beneden's Tubularidan from the true Tubularice, Agassiz seems 

 to me to be fully justified ; but I cannot so easily assent to the cor- 

 rectness of associating with it in the same genus the Sarsia pulchella 

 of Forbes, the Sarsia turricula of M'Crady, and the Sarsia nodosa 

 of Busch. (See Contr. Nat. Hist. U. S. vol. iv. p. 343.) These 

 naked-eyed Medusae are very different from the Medusae of Van 

 Beneden's Tubularia Dumortieri, while one of them (Sarsia turricula) 

 has been traced by M'Crady, if not with absolute certainty, at least 

 with high probability, to a Coryniform trophosome. 



Eetopleura Dumortieri, Van Ben. (sp.), = Tubularia Dumor- 

 tieri, Van Ben. 



3. Hybocodon, Agassiz. 



Trophosome, — Coenosarc invested by a chitinous periderm, 

 and consisting of a simple (or branched?) hydrocaulus rooted 

 by a filiform hydrorhiza. Polypites flask-shaped, with the ten- 

 tacles arranged in two sets, — the proximal set long, and forming 

 a single verticil, the distal short, and arranged in two verticils. 



Gonosome. — Gonophores phauerocodonic, springing directly 

 from the body of the polypite between the proximal and distal 

 sets of tentacles*. Medusa, at the time of liberation, with a 

 deep-belled umbrella, a moderate-sized, simple-mouthed manu- 

 brium, four radiating canals, and with the distal extremity of 



* In Hybocodon prolifer, the only described species, "the first Medusa 

 arises directly from the actinal area of the disc, while from the marginal 

 termination of one of the radiating tubes of this Medusa numerous similar 

 Medusae are developed, the latter again giving rise to other Medusae in the 

 same manner, and from a corresponding place on their margin." (Agassiz.) 



