Deep-sea and Shallow-water Hydrozoa. 11 



portant points from the * Challenger ' type specimens. They 

 consist of simple unbranched stems, the larger of which are 

 about 70 millim. in height, and they are thus destitute of the 

 characteristic habit which marks the old specimens of the 

 species. The type specimen figured in the report on the 

 * Challenger ' Plumulariidse was full-grown and evidently an 

 old specimen, while the present specimens are but young- 

 forms. With the exception of this difference of habit, due to 

 age, and of a slight difference in the corbula, the forms agree 

 in every essential respect. The difference in the corbulse 

 presents itself in their variable length. Sometimes the cor- 

 bula is composed of a few pairs of leaflets, especially in those 

 at the distal parts of the colony, where there are usually 

 about six or seven pairs, while again there may be present a 

 large number of pairs, ten or more, which are chiefly placed 

 on the proximal parts. The shape of the corbula conse- 

 quently varies considerably, from a rounded oval to a narrow 

 cylindrical form, the one passing insensibly into the other. 



In essential characters this species seems to be extremely 

 close to A. tuhuUferaj A. calamus^ and A. rigida. 



Streptocaulus pulcherrimus. (PI. I. fig. 5.) 



Streptoeaulus pulcherritnus, Allman, 'Challenger' Hydroida, pt. i. 

 p. 48, pi. xvi. figs. 1-3. 



Of this beautiful and extremely interesting form five 

 colonies were obtained, one of which attains a height of about 

 30 centim. They are especially interesting since they supply 

 the characters of the gonosome which were wanting in the 

 ' Challenger ' specimens, while at the same time the origin of 

 the spiral arrangement of the hydrocladia from the pinnate 

 form is clearly seen at the proximal parts of the colonies. In 

 some of the colonies the hydrocladia are absent from the basal 

 part for a distance of about 5-8 centim., while in others they 

 are continued nearly to the extreme base. These basal 

 hydrocladia are confined to one side of the stem and are 

 alternately arranged on each side of a line of more or less 

 rounded adnate nematophores, and spread in opposite direc- 

 tions, thus having a strictly pinnate disposition. Above this 

 basal part the planes of the hydrocladia gradually become 

 closer, until the hydrocladia become placed in one and the 

 same plane intermediate between their former positions, and 

 are attached not on each side, but in the direct line of the 

 nematophores of the stem. The torsion of the stem now 

 gives the spiral arrangement which is so distinctive of this 

 form. In the dried state this spiral arrangement is scarcely 



