PROF. ALLMAN ON STEPHANOSCYPHUS MIRAB1LIS. 65 



nected with one another by an extension of the ectoderm, we should have the tentacular 

 crown of the hydranth converted in nearly all essential points into the umbrella with the 

 radiating canals of a medusa. 



Now in certain species of Hydroida (Laomedea flexuosa for example) the tentacles are 

 actually connected at their bases by an ectodermal web. Here, then, there is little 

 needed to render the parallelism complete but the presence of a circular canal. Ste- 

 phanoscyphus, however, supplies the missing element, and, by the addition of a well- 

 developed circular canal, beautifully confirms the view here taken of the homological 

 relations between hydranth and medusa. 



Whether the relation between Stephanoscyphus mirabilis and the sponge with which 

 it is found associated is one of parasitism, or whether the association is merely acci- 

 dental, it is at present impossible to say. At all events, in no instance did I meet with 

 the Stephanoscyphus free from the accompanying sponge. 



From the account now given it is obvious that Stephanoscyphus must form the type 

 of a distinct order of Hydrozoa. "With the order Hydroida it possesses very decided 

 affinities, but it is nevertheless removed from the Hydroida by a distance at least as great 

 as that which separates these from the Siphonophora. For the new order I propose the 

 name of Thecomedus^ ; and if we bring together the characters given above, so as to 

 enable us to assign to Stephanoscyphus its true systematic position, we shall obtain 

 the following diagnostic category : — 



Subkingdom CCELENTEEATA. 

 Class Htdrozoa. 

 Order Thecomedus^:. 



Thecomedtts^:. 

 Animal composite, zooids medusiform, with circular and radiating canals, and included 

 in a chitinous rooted perisarc, which forms thecse, within which they are retractile. 



Genus Stephanoscyphus. 



Name from orecjyavoc, a crown, and <r/c{«£oc, a cup, in allusion to the cup-like body with 

 its crown of marginal tentacles. 



Gen. char. — Terminal orifice surrounded by a single circlet of simple filiform contractile 

 tentacula ; four longitudinal canals ; velum and manubrium undeveloped. 



Generative elements formed in the walls of the longitudinal canals ? 



Stephanoscyphus mirabilis. 



Perisarcal tubes springing from a basal tubular plexus, and rising to a height of about 

 one third of an inch, simple, rapidly enlarging upwards, annulated for some distance 

 from their distal extremities ; tentacles about 36 in number. 



Habitat. — Immersed in the substance of certain corneous sponges. 



Locality. — Antibes, Mediterranean coast of France. — G. J. A. 



SECOND SERIES. — ZOOLOGY, VOL. I. K 



