REPORT ON THE SIPHONOPHOR^E. 63 



Sexual Siphons (sx, figs. 2-5). — A great number of sexual polypites, densely 

 crowded and arranged in four to five concentric rings, occupies the broad basal zone of 

 the subumbrella, between the central siphon and the corona of tentacles ; their number 

 may be between sixty and ninety in the smaller, two hundred to three hundred in the 

 larger specimens. The form of these contractile gonostyles is very variable, usually 

 spindle-shaped or pear-shaped. The large sterile central siphon is eight to nine times as 

 long and five to six times as broad as each of the small fertile peripheral siphons. Their 

 mouth is small and exhibits eight radial lappets. The basal part is densely beset with 

 medusiform gonophores. 



Tentacles (figs. 2-4, t). — The corona of tentacles occupies a broad equatorial zone, 

 nearly half the height of the entire subumbrella. After removal of the tentacles 

 (fig. 3) this zone appears as a convex elegantly reticulated girdle, the concave inside of 

 which embraces the inferior half of the campanulate pneumatocyst (fig. 4, p). Each 

 rhomboidal mesh of the reticulum is the basal insertion of one tentacle. There are 

 eight to ten transverse rows of tentacles, one alternating with the other, and each row 

 represents a ring composed of fifty to sixty tentacles, so that their whole number may be 

 four hundred to six hundred. The length of the longest (in the middle zone) surpasses 

 the greatest diameter of the umbrella, whilst the length of those placed in the superior 

 and inferior rows decreases towards the limits of the tentacular zone. The tentacles are 

 slender cylindrical filaments, club-shaped at the distal end, and beset with three rows of 

 cnidospheres (compare above, pp. 38, 39). 



Subfamily 2. Porpitellid^e, Haeckel. 



Genus 5. Porpitella, 1 Haeckel, 1888. 

 Porpitella, Hkl., System der Siphonophoren, p. 30. 



Definition. — Porpitidse with a flat discoidal umbrella, including a circular discoidal 

 pneumatocyst without marginal lobes. Tentacles numerous, arranged in eight or sixteen 

 prominent radial bunches. 



The genus Porpitella and the following Porpita together make up the subfamdy 

 Porpitellidse, characterised by a discoidal or sbghtly vaulted umbrella, which includes a 

 discoidal pneumatocyst, the distal margin of the latter being circular, not divided into 

 radial lobes. The numerous marginal tentacles in Porpitella are arranged in eight or 

 sixteen regularly disposed radial bunches, whilst in Porpita they are ecpually distributed 

 along the margin of the umbrella. 



The new genus Porpitella is founded for those species, formerly placed among 

 Porpita, which are distinguished by the possession of sixteen radial bunches of marginal 



1 Porpitella = Small ring of a buckle, diminutive of Porpita. 



