78 The Genera of the Plumulariidce, 



•equivalent to a separate shoot of such species as A. parvula, 

 a fact which is further illustrated by the presence, near the 

 base of the stem in the latter species (and, indeed, in many 

 others), of a long oblique joint similar to that which exists 

 near the base of each pinna in A. longicornis. Such a 

 joint is seen in young specimens of ^. divaricata, and when 

 the supplementary tubes grow up, and branches are pro- 

 duced, each branch has a similar joint. I have not hitherto 

 met with any species with branches springing both from the 

 jointed stem and the added tubes. 



ELEUTHEROPLEA. 



Plumularia, Laonk, modified. 



Hydrocladia pinnately arranged ; sarcothecse not attached 

 to the hydrotheca. 



Gonangia not provided with phylactocarps. 



Lamarck's genus Plumularia was originally formed to 

 include the whole of the pinnate Plumularians, and was 

 synonymous with the Aglaophenia of Lamouroux. The 

 latter author, however, suggested a subdivision of the genus, 

 which was adopted by M'Crady and later authors, and in 

 which the name Plumularia was assigned to the Eleuthero- 

 plean species, and Aglaophenia to the Statoplean. Accord- 

 ing to Professor Allman's views the genus should be still 

 further limited, so as to include only those species with all 

 the sarcothecse movable ; and in the " Challenger" Report 

 he proposes a new genus — Heteroplon — for a species which 

 has the anterior sarcotheca in the form of a stout fixed 

 spine, curved towards the hydrotheca. This condition of 

 the sarcotheca, however, is common to several of our species, 

 while in others it differs from that of a typical Plumularia 

 only in its stouter base and consequent wider area of attach- 

 ment, which renders it rigid. Every possible degree of 

 variation exists between the long, slender sarcotheca, which 

 is swayed by every motion of the fluid surrounding it, and 

 the short fixed spine of Heteroplon pluma ; it follows, there- 

 fore, that there is no definite line of demarcation between 

 Heteroplon and Plumularia. Of the species described in 

 the " Catalogue," P. Ramsayi, P. cornuta, P. setaceoides, 

 P. effusa, P. ohliqua, P. spinulosa, P. hyalina, P. pulchella, 

 and probably P. hadia, have the anterior sarcothecse per- 



