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



term, "shark-skin "), this is of some little value. The skins of other kinds, however, 

 including C. squamosus, are only fit for polishing wood, for which purpose the skin 

 is dried and cut into long narrow strips. One such skin, the species being Sci/mmis 

 lichia, was purchased by Dr. Vaillant for a franc and a-half, or thereabouts. 



The liver yields an oil used by the country folk in their lamps, and parti- 

 cularly esteemed for the lubrication of wooden machinery. Finally the body of 

 the fish is dry-salted and used for food just as our most familiar member of the 

 family, Acanthias vulgaris, is used on the Cornish coast. 



It is hardly to be wondered that Vaillant doubts how far such products would 

 indemnify the cost of the gear and fittings necessary for such a fishery, and we 

 have no reason to suppose that the inhabitants of the Mayo coast are ever likely 

 to put the matter to a test ; but there is no doubt, as Vaillant remarks, that 

 similar gear might with advantage be used for scientific purposes, with a view to the 

 discovery of forms not likely to be captured in trawls or dredges. 



Batoidei. Rays. 

 Genus Raia, Cuvier. 



Remarks on the Diagnosis of Species belonging to the Genus Raia. 



The variation which is found amongst the species of this genus has proved a 

 source of considerable perplexity and error to many observers. 



The difficulty of identifying certain species is very great, and arises not only 

 on account of the variation, but also because a custom has become established 

 amongst writers to include in their diagnoses certain features which alter, to an 

 extraordinary extent, according to age or sex. The relative convexity of the 

 anterior margin of the disk, the arrangement of the dorsal and caudal spines, and 

 the colouration and markings of the back may be taken as examples of the varying 

 features referred to. The number of rows of teeth are generally looked upon as 

 of paramount importance in the identification of species, but even here we find 

 that considerable modification exists according to the age of the specimens 

 examined. 



It is therefore not surprising that in the descrijitions of species from a limited 

 number of examples at command, statements should have been made which in 

 reality are applicable only to one sex at a certain stage in its existence, instead of 

 applicable to the species as a whole. 



When comparing mature examples of any species, a marked difference may at 

 once be detected between the males and the females. The presence of claspers, 

 and alar spines in the males alone, have always been recognised by writers, but 



