EEPOET ON THE SIPHONOPHOR^E. 67 



inerme. Tentacula marginalia trifariam glandulosa." He described five different species, 

 Two of these only appertain to the genus Porpita as above defined (Porpita mediter- 

 ranea and Porpita umbella). 



The best and most accurate anatomical descriptions of the genus are those given in 

 1853 by Kolliker of Porpita mediterranea (4), and in 1881 by Alexander Agassiz of the 

 North Atlantic Porpita linnseana (57). Closely related to the latter is probably the 

 tropical Atlantic Porpita umbella of Eschscholtz (1). The collection of the Challenger 

 contains several specimens of a new species, taken in the Northern Pacific, and figured 

 in PL XLV. as Porpita fungia. Three other distinct species seem to be Porpita liitkeana 

 (25), from the Indian Ocean ; Porpita pacifica of Lesson (22) ; and a new southern form, 

 Porpita australis. 



The phylogenetic origin of Porpita is to be found in the preceding genus, Porpitella, 

 from which it is derived by multiplication and equalisation of the tentacles, not forming 

 separated radial bunches. 



Porpita fungia, n. sp. (PI. XLV.). 



Habitat. — Stations 253 to 255, Northern Pacific, between Japan and Honolulu; 

 14th to 19th July 1855; lat. 38° 9' N. to 32° 28' N., long. 156° 25' W. to 154° 33' 

 W. Surface. 



Umbrella (fig. 1, meridional vertical section). — The disc is flat, circular, of equal 

 thickness throughout nearly its whole extent, like a coin. Its diameter is usually 20 to 

 25 mm., but amounts in the largest specimens to 30 mm. ; its thickness (without the 

 siphon and tentacles) is 4 to 6 mm. A meridional section (fig. 1) demonstrates that 

 three-fourths of the thickness belong to the centradenia, one-fourth to the pneumatoc3 7 st. 



Exumbrella (fig. 2). — The superior or apical face of the umbrella is flat or slightly 

 convex, a little depressed in the centre. It is covered with numerous, irregularly scat- 

 tered, Gonical tubercles, arising from the upper face of the pneumatocyst. Their number 

 and size increase towards the centre. The peripheral half of the exumbrella is pierced 

 by numerous irregularly scattered stigmata (p>e). The regular octoradial striation and 

 the numerous concentric rings, which shine through the silvery exumbrella, are due to the 

 structure of the subjacent pneumatocyst. An elegant network of anastomosing canals, 

 with narrow irregular polygonal meshes, is expanded everywhere in the exumbrella. 



Limbus Umbrellas. — The free membranous border or limbus of the umbrella overlaps 

 the tentacular zone to the extent of 1 to 2 mm. It is flatly expanded or reflected 

 upwards, and includes a series of marginal glands of the usual form (compare above). 

 The numerous canal-branches of the exumbrella anastomose richly, form an irregular 

 network, and unite in a circular canal inside the glandular corona ; and from this arise 

 the vessels of the centradenia and the subumbrella. 



