258 M. MIYAJIMA : 



one curious point of difference between our specimen and 3fono- 

 caulus Imperator. While the hydranth in the Challenger speci- 

 men is much smaller than that of our specimen, the stalk is 

 enormously longer, being said to reach the almost incredible 

 length of 7 feet 4 inches. This is, however, stated to be when 

 stretched, and is not the normal length. 



While it is not thus possible to establish absolutely the 

 identity of our specimen with 3Iouocaulus imperator of Allman, 

 there are on the whole strong probabilities in favor of this 

 assumption. Those who read carefully Allman's description will 

 notice that the points which he brings out distinctly in the 

 structure of his species, such as a wide cavity extending through 

 the entire length of the stalk, the presence of the stalk-mesoderm 

 in the shape of a fibrillated membrane — a point which Allman 

 emphasizes as *' the most striking feature in the histology of the 

 Hydroid " — and so forth, are absolutely similar in our specimen. 

 If we remember in addition that both came from practically the 

 same locality, it is, I believe, within the scope of reasonable- 

 ness to conclude that our specimen belongs to 3Ionocaulus imperator 

 of Allmann. 



If this is really the case, we must examine other species in 

 3ïonocaulus. The genus includes, besides Monoca^ilus impe7'ator, 

 two other species ; 31. glacialis, (Sars) (for which Allman esta- 

 blished the genus) and 31. pendula, (Agassiz). These two forms 

 show, however, a radial symmetry, and now that 31. imperator 

 is shown to have a bilateral symmetry, can not possibly be put 

 in the same genus with the latter. 31. imperator must therefore 

 be separated from the other two species and placed in a new 

 genus. According to the rules of nomenclature, this new genus 



