384 Survey of Fishing-Grounds, West Coast of Ireland, 1890-1891. 



what similar to that seen in a young male, R. circularis ; but if adults of both sexes 

 be examined, a much greater contrast is found than exists in adult R. circularis as 

 seen in fig. C. Taking a transverse section of the tail in both sexes, we present 

 figs. D and E. 



(c). Coloration, and markinffs of the skin. — It is a matter of common knowledge 

 that colour variation, so frequently met with in fishes as a whole, is, at least, 

 as frequent amongst the Raiidae as in any other group. Nevertheless we in- 

 variably find a more or less precise statement of the pigmentation included in 

 diagnoses of the species of this family. To eliminate such altogether is by 

 no means desirable, but it is certainly necessary to allow great latitude of inter- 

 pretation to existing descriptions. 



The names R. alba and R. maculata indicate that both general colour and parti- 

 cular markings have been considered characteristic features of certain species ; 

 and in the case of R. alba we know that the dead whiteness of the ventral surface, 

 which is certainly characteristic of the adult, has been found to be constantly 



D E 



DiAG. 3. — B represents the condition found in adult females — one row of median spines, with two rows on each 

 side. E is produced from nine examples of adult males, seven of which possessed the median row 

 of spines alone, the other two specimens haying, in addition, a few isolated spines on one side. 

 The latter are indicated by the dotted spines. 



diversified by bands of brown in the young. In R. maculata, again, we have 

 observed a specimen in which the spots were wholly absent. The alar ocellus, 

 which is so conspicuous in the Cuckoo Ray, is represented to a greater or less 

 extent in the young stages of nearly all species of Raia which have come under 

 our notice ; and since it may be either very conspicuous or hardly discernible in 

 the adult condition of a single species {e. g. R. maculata), it is evidently a character 

 which should not be very strongly insisted on in specific diagnosis. 



The wliiteness of the ventral surface which characterizes the living condition 

 of a great many ra^'s is subject to considerable post-mortem changes, since it may 

 become grey, or even brownish, when the fish has been dead for some time. Post- 

 mortem, changes are also noticeable in the general texture of tlie skin, owing at 

 least in great measure to the drying influence of the atmosphere. Thus, a 

 fish which, when fresh, appears perfectly smooth both to sight and touch, may 

 be found, when stale, to be covered with minute asperities, imparting to the skin 

 a distinctly granular appearance ; and it seems very probable that a want of 



