REPORT ON THE HYDROIDA. 
79 
somewhat curved, compressed, and pod-shaped form of the gonangia will, however, at 
once distinguish it. The specimens in the collection have a height of more than two 
inches. The main stems arise from a prostrate, branched, tubular filament, and while 
they are themselves unbranched are set from end to end with exactly opposite pinnae. 
A joint more or less distinct exists on the stem at the distal side of every pair of pinnae. 
With the exception of an occasional pair of hydrothecse in the interval between two 
pinnae, no hydrothecae are borne by the stem. The pinnae are given off at a very wfide 
angle, being nearly at right angles with the stem. They are divided by deep con- 
strictions into short equal internodes, each internode carrying a pair of exactly opposite 
hyclrothecae. The hydrothecae are deep, tubular, adnate to the internode for about two- 
thirds of their height, and then abruptly divergent at a high angle. The orifice is 
perfectly circular, and its margin entirely destitute of serration. 
The gonangia are usually, but not exclusively, carried by those hydrothecae which 
lie near the base of the pinna. They have the appearance of being absolutely sessile 
on the summit of the hydrotheca. In reality they have a long peduncle which passes 
down through the hydrotheca and completely fills its cavity. They would seem to 
differ in the two sexes. Those w r hich I regard as female (fig. lc<) are compressed, so as 
to be elliptical in transverse section, are slightly curved towmrds the axis of the pinna, 
and are very elegantly ornamented on the two broad faces by prominent, transverse, 
parallel ridges, which gradually thin away towards the edges, where they become 
finally effaced. Gonangia which differ from these in form were present in one 
specimen (fig. lb). I regard them as those of a male colony. They are oviform, with the 
axes straight, and are destitute of the ridges w r hich form a characteristic feature in the 
others. Both forms of gonangia open on the summit by a small, scarcely elevated, even 
orifice. 
In one of the specimens of Synthecium campylocarpum in the collection no 
gonangia w r ere present ; but the place of a gonangium was taken by a branch w T hich 
thus had its origin within the hydrotheca, from the orifice of which it protruded (fig. lc). 
This branch carried pairs of opposite hydrothecse, and differed in no respect from an 
ordinary pinna. 
Though I regard this as an entirely abnormal condition, it is by no means destitute 
of morphological interest as repeating in Synthecium a feature which constitutes the 
essential character of Thecocladium ; while the substitution of a typical nutritive 
element of the colony for a typical reproductive one is not without significance. 
Synthecium has been hitherto known only as a New Zealand genus, Synthecium 
elegans being apparently an abundant and characteristic species of the New Zealand 
coast. The same haul of the dredge, however, which brought up Synthecium campylo- 
carpum from a depth of between 30 and 35 fathoms off Port Jackson, yielded also 
Synthecium alternans, another very distinct and interesting member of the genus. 
