Among the Siboga material were specimens which fitted sufficicntly to each of these 

 formulae (except for the large number of jaws ui ?iiagna Grassi). On adding to them specimens 

 of magna supplied from the Zoological Station at Naples, one feit fairly confident that one 

 had all the species before one. Good .specimens were selected and compared, with the result 

 that no specific difference could be detected between them : in all ordinary characters such as 

 the position and extension of the fins, the size and position of the abdominal ganglion, the 

 extension and shape of the corona, the proportion of tail to triink, and so forth, they were 

 practically identical ; the vestibular ridges, and even the tips of the younger jaws, were of the 

 same character. I have no doubt that hexaptera d'()rbign\, magna Langerhans and tricuspidata 

 Kent, forni one species. Whether magna Grassi is the same or not, is not so easy to sa\' : some 

 of my specimens showed nine jaws with a rudimentary tenth, but ten was the outside number 

 observed. But as the .specimens of "■magna" sent from Naples were undoubtedly he.xapteran, 



it is probable that Grassi had before him specimens of licxaptcra with numerous jaws and 

 few teeth; such occur in the table below. 



Since there is practically nothing in their original definitions to differentiate magna anti 

 tricuspidata from one another and from Jiexaptera except the formulae for armature, it is 

 necessary to show the resemblance between specimens which conform more or less to the 

 formulae; this has been done on ];late I. The outlines of the entire animal ') (figs. 30, 34, 38) 

 are as alike as could be expected in three different specimens of the same species; the iwo 

 coronae (figs. 35, 39) agree with each other and with lluil figured by Hkrtwig for Itcxaptera 

 (op. cit., ])1. I\\ fig. 21); those of the distal end of the latest (most anterior) jaw agree in 

 the characteristic outline first recorded by Krumbach (Über die Greifhaken der Chiitognathen. 

 Zoologische Jahrbücher, Abtheilung Systematik, u. s. w., X\'III, ]j. 579, fig. P.); if the figures 

 of the anterior and posterior teeth do not at fir.st sight agree equally well, the failure must be 

 attributed to the impossibility of getting them to lie at precisely similar angles, and to the 

 inability of the draughtsman to represent properly the consecjuent foreshortening. By focussing 

 it was apparent that they belonged to the same type, — a broad base from which rises an 

 unusually long and slender tooth. In such large, and therefore opaque, heads as most hexaptera 

 present, it is generally impossible to see the whole of the vestibular ridge under the microscope 



1) .\s typical specimens of masfiia wcrc only nolicod in tlic alcohol material, the oiitliiie for lliis "species" has been taken 

 from a Naples specimen. 



