31 



resemble Z. niegnstonm, but it is scarcely probable that this species, already 

 when it is 19 mm long, should lose its spiuey uear Ireland, wheu it keeps 

 them iu the neighbourhood of Iceland till it is as long as 27 mm. I take 

 it for granted, bowever, that such a skilful investigator as HoU cannot have 

 overlooked the spiues, if they had been there; and it struck me, tlierefore, 

 that at least his small specimens without spines do not belong to Z. tnega- 

 stoma at all, but to auother species. When this doubt had ou'ce risen 

 in m}' mind I saw that Holt himself (1. c. page 74) is astonished that 

 the small young oues resemble "RIio»ihus hoscii (Risso)" much more thau 

 Z.megastoma: but he supposed that tliis would change later on. No, this 

 supposition is scarcely correct; for this little, 19 mm long young one, 

 table I, fig. 11, is fully developed with persistent pectoral rays and large 

 e3'es, as the grown-up fish. It will hardly change its form. But it agrees 

 in form ver}' closely with '■Jthomhiis hoscii (Risso)", as Holt himself says, 

 and is much liigher over the pectoral fius thau Z. megastoma. In order to 

 obtain better information of the Irish ''JRhonibus hoscii' I asked Holt to send 

 me a grown-up specimen, and he was kind enough to do so. I had thus 

 an opportunity to see that this small species (c. 20 ctm. long) in the form of 

 its body and size of its eyes agrees vei-y closely with my fig. 11, which I 

 have copied from Holt, and that it was a true Zeugopterus, not a Ehomhus, 

 for it had a perfoi-ated isthnnis like tlie other species of Zeugopterus. Because 

 it is a smaller specimen, probably, it loses its spines at a shorter length 

 than Z. megastoma, and this, I think, explains why Holts figures 116 and, 

 perhaps, 117 have no spines. In "Ann. Mag. Nat. Hist.", December 1889, 

 page 418, Giinther has given the correct information that the large eyes are 

 cliaracteristic of Z. hoscii in contradistinction to Z. megastoma: but I shall 

 here caution against a comparison between ray figures 11 & 10, as the latter 

 belongs to a larval stage (the pectoral fins) while figure 11, on the other 

 band, is fully transformed. I do not possess any Z. megastoma beionging to 

 a stage corresponding to figure 11. Loc. cit. Giinther says that both the 

 said species have vomer-teeth, and therefore, properly, ought to he removed 

 from the genus Arnoglossus, to which he has provisioually referred them. 

 This is quite coi-rect, of course. They are, both of them, true species of 

 Zeugopterus, as we now kuow. 



According to the above it must l)e considered the rule then, that the 

 larvæ of the genus Zeugopterus, at a certain stage of their lives, liave "oto- 

 njstic" spines, i. e. a pair of spines on either side of the head, in tlie ear- 

 region. We know only one exception from this, Z. norvegicus, wluch as a 

 young fisii has no such spines at all. This agrees very well with the faet 

 that this species, as H. M. Kyle has verbally informed me, from osteologic 

 and otlier reasons, must l)e imagined to he the one wliich is fartliest removed 

 from tlie cither species of the genus Zeugopterus. 



