HYDROZOA — RITCHIE. 853 



inches long, and named by him Plumularia aglaophenoides. The 

 recent examination of the original specimen in Lamarck's type 



-collection by Dr. Armand Billard leaves no doubt that this 

 species is identical with Fhcnndaria sulcata, Lamarck, and the 

 *' Thetis" specimen agrees even more closely with Billard's 



• description of Lamarck's type than does that of Bale. The 

 f i-agmentar}'^ nature of Bale's specimen and the no less imperfect 

 condition of the type, which is recorded as 15 or 16 centimetres 

 long, offer excuse for a more complete description of the macro- 

 scopic aspect of the colony. 



Trophosome. — The stem is polysiphonic and stout, 3'5mm. in 

 •diameter at the base, and is straight and rigid. Although obviously 

 incomplete, it attains a height of 28 cm. and bears four irregu- 

 larly-placed branches, 2 mm. in basal diameter, the lowest of 

 which springs from the stem 16 cm. from the base, and all of 

 which lie in the same plane. Stem and branches are sinuous — 

 though never sufficiently so to dispel the impression of straight- 

 ness which the sturdy portions convey — and from the summit of 

 ■ each wave springs a primary hydroclade bearing both hydrothecse 

 and secondary hydroclades. The primary hydroclades thus lie 

 in one plane, alternating in a pinnate series. Two primary 

 •hydroclades on the same side of stem or branch are distant from 



• each other about 6-5 mm., and their length varies from 15 to 

 20 mm. The lax, scraggy appearance of the colony is well 



•described by Lamai'ck : — " Cette espece est maigre, lache dans 

 toutes ses parties. Sa tige et ses branches ofFrent des sillons 

 ascendans et ondes."*-^ 



The stem-fascicle is formed of stout tubes, each of which is 

 armed with a series of opposite sarcothecse, similar in structure 

 to that which lies proximal to a liydrotheca. On the tubes which 

 issue from the fascicle as primary hydroclades, this paired series 

 ■commences proximal to the lower of the two markedly oblique 

 joints with which the pinna originates ; and here the tube is 

 divided into a small number of internodes of irregular length. 

 Not only does the internode included between these oblique joints 

 bear sarcothecse, as both Bale and Billard remark, but in tlie 

 present specimen it bears a rather undersized hydrotheca, and is 

 ■exactly like the succeeding thecate internodes, even giving rise, 

 in many cases at least, to a secondary hydroclade. Occasionally 

 hydrothecate internodes, bearing paired sarcothecse, interrupt 

 the hydrothecate course of the primary hydroclades. 



The median sarcothecse which lie behind a hydrotheca in the 

 axil between it and the hydroclade are rudimentary structures, 



*■"' Deshayes and Milne Edwards ed. of Lamarck, ii. edition, 1835, ii., 

 J). 164. 



z z 



