ATLANT. DEEP-SEA EXPED. 1910. VOL. Ill] 



HYDROIDA. 



in accordance with nomenclatorial rules the name of 

 Klrchenpaueii must be dropped, and I have in a previous 

 paper 1 ) proposed the name of septifera on account of 

 the characteristic intrathecal septum which so markedly 

 distinguishes the species from the pluma-gwup. 



Aglaophenia tubulifera Hincks. 



Near Cape Bojador, abundant and fertile in 39 metres 

 (Stat. 37); a single sterile colony from 77 metres (Stat. 38). 



Fertile colonies of this species are easily recognised 

 owing to the detachment of the basal pair of leaves which 

 hang outwards and downwards, whereas the other leaves 

 are coalesced so as to form the sides of the corbula. 

 Only a single hydrotheca was found between the 

 corbula and the stem. 



The internodes of the stem are provided with 

 only three nematothecae, a mesial one ventrally 

 (anteriorly) near the proximal end of the internode, 

 and a pair on the distal side of the hydrocladial 

 base (see fig. 9, a, in which the hydrocladial base 

 hides one of the paired nematothecae). 



Two other species from the Atlantic must be 

 regarded as synonyms of Aglaophenia tubulifera, 

 viz. Aglaophenia insignis Fewkes, and Aglaophenia 

 elegans Nutting. A first glance at the figures in 

 Nutting's work 2 ) seems to reveal very great diffe- 

 rences, and we might from this be inclined to consider 

 them as "good species". But a closer examination 

 of further material shows every transition stage, and 

 it is rather curious that the very characters which 

 served Nutting as a basis in his separation of 

 groups turn out to be the most variable characters 

 of all. As a specific character Nutting uses the angle 

 between the mesial nematophore and the hydrotheca. If 

 we study a somewhat larger hydrocladium, we see that 

 not only is this angle subject to great variations/but also 

 that the variations follow easily distinguishable rules. The 

 angle between the nematophore and the hydrotheca in 

 the distal parts of the hydrocladium is acute (fig. 9, b), 

 whereas it is more of a right angle the nearer we approach 

 the base of the branchlet (fig. 9, c). Thus in specific 

 diagnoses this character must be used with the utmost 

 caution. Another character used in the separation of 

 groups reads: "free portion of mesial nematophore longer 

 than width of hydrotheca." A glance at figs. 9 b— e will 



soon convince us of the value of this character, which by 

 the way is a gradual one, for the hydrothecae b, c, and 

 d are from colonies budding on the same stolon, b and c 

 from the very same hydrocladium. 



It is probable that Aglaophenia tubulifera is the only 

 species hitherto known from the Atlantic, having the 

 proximal leaves of the corbula detached from the others 

 and hanging outwards and downwards. Billard, 3 ) who 

 has studied the variations in this species and has had an 

 opportunity of re-examining many of Allman's type-speci- 

 mens, 4 ) has proved the identity of Aglaophenia filicula 

 Allman, with A. tubulifera. 



In his excellent paper on the hydroids of the "Tra- 



Fig. 9. Aglaophenia tubulifera. a: portion of the stem showing the 



arrangement of the nematothecae on the internodium; b— e: hydrothecae 



(see text), a-d from Stat. 37, e from Stat. 38. (X 60). 



vailleur" and "Talisman" expeditions, Billard (1. c. p. 233) 

 describes a variety of Aglaophenia tubulifera with extre- 

 mely long nematophores. A single colony of this variety 

 was taken by the "Michael Sars" (fig. 9, e), and interme- 

 diate stages between the variety and the typical Aglao- 

 phenia tubulifera seem to be very rare. I propose to 

 name the aberrant form with long nematophores forma 

 Billardi in honour of their discoverer, the form with short 

 nematophores being regarded as the forma typica. Probably 

 the degree of development of the mesial nematophore is 

 due to the direct influence of biophysical factors, regarding 

 which we are at present in the dark. 



x ) Hydroiduntersuchimgen III, p. 61. 



2 ) American Hydroids I. The Plumularidae, plate XIX, figs. 3 — 7. 



3 ) Hydroi'des (Exped. scient. "Travailleur" et "Talisman"). Paris 1906. 



') Revision d'une partie de la collection des hydroi'des du British Museum (Ann. des. sci nat., Serie 9, Tom. XI). Paris 1910. 



