﻿144 



PROCEEDINGS OF THE 



[April, 1857. 



a coincidence enhances the probability that my suggestion will 

 prove correct. 



Distribution. — The genus Porpita is found in the Mediterranean, 

 and appears to be distributed in ali the tropical oceans extending 

 north or south of the equator, probably not more than 40° either 

 way; though being a floating genus it is probably frequently 

 driven to higher latitudes by storms. 



PORPITA LINNEANA. Lesson. 

 Syn. Polybrachionia Itinneana. Landsdown Guilding. Zool. Journ., vol. XI, p. 

 403. — {Quoted from Lesson.) 



The form of the imperfect Medusa above mentioned is a four- 

 sided pyramid, whose altitude is about equal to the width of its 

 base, or slightly exceeds it. The uncolored parts are very trans- 

 parent so as not to he easy of definition. The digestive trunk is 

 of an earthy red, the lower portion of the radiate tubes of a reddish 

 orange color. The digestive trunk was quite short and confined 

 to the upper part of the yet unopened bell-cavity. 



The Larval community is almost exactly of the size given by 

 Guilding, that is, the whole disk, including the border, is generally 

 about an inch in diameter. Sometimes, however, a large specimen 

 will have an air-shield nearly an inch in diameter without the bor- 

 der which is in width between a tenth and two-tenths of an inch. 

 When viewed in profile it is seen that this air-shield is not 

 perfectly flat but that the centre is very slightly elevated above the 

 border. The longest marginal tentaculiform organs are in length 

 about equal to the diameter of the disk. They are, however, of 

 three or four sizes, the smallest not emerging from under cover of 

 the border. These tentaculiform organs are not straight hut 

 curve upwards at the end. The pedunculated buttons or knobs 

 on the longest are further apart than on the shorter ones. Next 

 beneath and within are the Medusa-bearing individuals. They 

 are generally slender and tapering, the mouth appearing to be 

 simple like that of the digestive polyp of Physalia, not cloven 

 into lips as represented by Kolliker in Porpita Mediterranea. 

 Only, when contracted, do they assume a sometimes flask-shaped, 

 sometimes almost globular form. The Medusa-buds are not con- 

 fined to the bases of these polyps but scattered over their length, 

 sometimes appearing not far from the oral extremity. The color- 

 ation of these buds when advanced, is so distributed as to mark 



