HYDROIDA II 



is attached. The hydranth has a proximal tentacle crown, the growth of which takes place from the 

 part of the hydranth periphery nearest the stalk, where the shortest tentacles are found. The tentacles 

 of the oral circle are homogeneously developed. The periderm of the stalk is reduced and soft. The 

 blastostyles are situate between the tentacle crowns, the youngest ventrally above the point of at- 

 tachment of the stalk. The polyps are solitary. 



Allman (1888 p. 5) described the first Branchiocerianthus species, which was brought home 

 by the "Challenger", under the name of Monocaulus imperator. The family Monocaulida had been 

 previously founded by A 11 m a n n (1871 p. 395) with the following diagnosis: "Hydrocaulus solitary, naked. 

 Hydranths with a proximal and a distal set of filiform tentacles. Gonophores in the form of fixed 

 sporosacs". This diagnosis thus makes no mention of the essential point, to wit, the bilateral character 

 of the polyp. Nor is any reference to this found under the heading of the only genus, Monocau- 

 lus, which is thus described: 



"Hydranth abruptly distinct from the hydrocaulus; proximal tentacles longer than the distal 

 and disposed in a single verticil near the base of the hydranth, the distal set scattered over a zone 

 close to the summit of the hydranth. Sporosacs borne upon peduncles, which spring from the body 

 of the hydranth between the proximal and distal sets of tentacles. 



The genus Monocaulus is constituted for the Corymorpha glacialis of Sars, a form which, 

 though its trophosome is that of a Corymorpha, is yet strongly distinguished from the true Corymor- 

 phas by its adelocodonic gonophores" (Allman 1871, p. 396). 



In addition to Corymorpha glacialis, Allman also places Corymorpha pendula L. Agassiz in 

 the genus, this being a species with free medusse. Later on, Corymorpha groenlandica is also placed 

 in the same genus. And here, finally, Monocaulus imperator is likewise included, Allman (1888 p. 5) 

 having entirely overlooked the bilateral structure of the species, and disregarding the morphological 

 peculiarities noted in his descriptions. 



With reference to Corymorpha I have pointed out that All man's typical Monocaulus, Cory- 

 morpha glacialis M. Sars must remain in the genus where M. Sars placed it, like Monocaulus groen- 

 landica Allman, the only species which entirely answers to the diagnosis given by Allman. It would 

 therefore be altogether wrong to follow the suggestion given in "Nornina conservanda" (cf. p. 53) and 

 retain the generic name Monocaulus for a genus where Monocaulus imperator has been somewhat 

 arbitrarily chosen as type, the more so since the essential feature of the species, which is even cha- 

 racteristic of the genus as a family type, was distinctly emphasised by E. L. Mark in 1899 in his 

 description of the central American Pacific species Branchiocerianthus urceolus Mark. Since then, the 

 genus has been referred to in all leading works under the generic name given it by Mark, Bran- 

 chiocerianthus, and as the species in question have been accorded only the briefest mention in the 

 handbooks, there will be no confusion caused by general adoption of the appellation. Moreover, after 

 the publication of the fundamental studies on Branchiocerianthus by Mark (1899), Miyajima (1900), 

 and Stechow (1908, 1909) it would certainly be confusing to adopt the name Monocaulus. 



The genus Branchiocerianthus was hitherto only known from the Pacific (Alaska, Japan, Pa- 

 nama) and the Indian Ocean (Beluchistan, Oman, and East Africa). Stechow, in his description of 



