264 bulletin: museum of compakative zoology. 



III. SIPHONOPHOEAE. 



Porpita lutkeana Brandt. 

 Brandt, 1825, Mem. Acad. Imp. St. Petersbourg Sci. nat. ser. 6, tome IV. 



Plate 7, Figs. 34, 35, 36. 



It i.s with considerable hesitation that I refer our specimens of this genus to 

 the Porpita lutkeana of Brandt, which seems, however, to fit them better tlum 

 any other described species of Porpita. The Pacific and Indian forms of the 

 genus have always been in confusion, owing to the fact that most of the early 

 descriptions are altogether insufficient for identification. Haeckel (Siphono- 

 phorae of the " Challenger " Expedition) recognizes, besides the well-known At- 

 lantic forms, Porpita lutkeana Brandt, to which he gives the synonym, Por[iita 

 indica (see iljid.); Porpita pacifica Lesson = Porpita gigantea Peron et Lesu- 

 eur ; Porpita australis Haeckel (System der Siphonophoren); and Porpita 

 fungia Haeckel (Siphonophorae of the " Challenger " Exped.). 



Porpita lutkeana agrees in general with our specimens, although Brandt's 

 description is so meagre that an accurate determination is very difficult. 



The disc, in the largest specimen, measured forty-five mm. in diameter and 

 five mm. in thickness. The upper, external surface of the exumbrella bears 

 a series of minute knobs and corrugations, making it rough to the touch. Tiie 

 central chamber and the eight larimary radial chambers are large, and com- 

 municate with the exterior by prominent stigmata. Over the rest of the exum- 

 brella the stigmata are very irregularlj' arranged. There are thirty-two circular 

 partitions, at nearly equal distances, dividing the pneumatocyst into as many 

 circular chambers, which are in comnuinication with each other through 

 openings in the circular partitions. The floor of the float cavity is thrown into 

 a series of deep radial furrows and ridges, which interlock with the underlying 

 ridges and furrows of the liver. These corrugations arise at the centre as eight 

 folds, which by branching come to number about sixty. In addition to tliese 

 and alternating with them, a series of shorter folds, arising at the periphery, 

 runs centripetal for a short distance between the original centrifugal ridges, 

 making the total number at the margin about one hundred and twenty. 



The liver is of considerable thickness, completely filling the space between 

 the bottom of the float cavity and the lower surface of the disk, where it com- 

 municates with the bases of the reproductive polypites. 



There are about two hundred tentacles, arranged in about four or five con- 

 centric rows, instead of the nine rows described by Brandt. When fully 

 extended they are about as long as the diameter of the disc. Each tentacle 

 bears three distinct rows of knobs, in the manner typical of the genus. At the 

 tip of the tentacle there is a cluster of four, and this number appears invari- 

 able. In each row there are about ten knobs. 



The central sterile polypite is large, with smooth walls, and very distensible. 



