NOTES AND MEMORANDA. 403 



of the mandible^ in such a position as to be almost masked by the 

 maxilla when the mouth is closed. The pre-operculum beai's short, 

 outwardly directed spines along the entire length of its keel, and 

 longer backwardly directed spines are present on its posterior por- 

 tion, the margin of which is also serrated. The free edges of the 

 sub-operculum and inter-operculum are strongly serrated near their 

 union. 



The spines above the eye seem the earliest developed, as they are 

 present even in my smallest example. The ridge on which they are 

 borne seems to represent the outer edge of the frontal scuta, which 

 must ossify at an earlier period than the rest of that structure. The 

 ridges of each side become opposed in tl^e process of metamorphosis, 

 and persist in the adult, but they lose their prominence and the 

 serration of the edges before the oldest stage in my series is reached. 

 The mandibular armature is early formed and early lost, but its 

 (apparent) position is marked in the adult by the strong lateral keel 

 of the articular. The opercular spines do not seem to be present in 

 the smallest examples, in which the scutes of this region are probably 

 not yet ossified. They reach their maximum development in speci- 

 mens of about 10 or 11 mm., and thereafter tend to disappear, 

 doubtless by the growth of additional bony matter around them. 

 The serrations of the sub-operculum and inter-operculum persist 

 longer than the rest, and are visible, though very blunt, in my 

 largest example. Indentations exist in the margin of these scutes 

 even in a specimen of 25 mm. kindly sent to me from Plymouth, 

 and very faint indications of the same can be made out in a speci- 

 men of 175 mm., though none are perceptible in adult specimens. 

 At no stage of which I have any knowledge is there any spinous 

 process or processes in the region of the otocyst, and this serves to 

 distinguish young turbot from certain of the small forms attributed 

 by Mcintosh and Prince (loc. cit.) to this species, and also from 

 some remarkable Pleuronectid larvae which were obtained during 

 the survey on the west coast of Ireland. Since the smaller larvae 

 briefly described by the Scotch authors are said to agree in pig- 

 mentation with those which exhibit spines on the otocyst, it seems 

 very unlikely that any of them are turbot, and therefore the North 

 Sea series which I have described above are probably the first 

 recorded examples at those sizes. 



It is interesting to find a Pleuronectid passing through a stage in 

 which its cephalic armature is as powerful as, and for the most 

 part homologous with, that of a Percoid or Scorpaenoid, though I 

 cannot call to mind any form in which the mandibular spines of 

 the young turbot are represented. Amongst Acanthopterygians we 

 are familiar with instances in which, while the head is practically 



NEW SERIES. — VOL. II, NO. IV. 31 



