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



the claspers are elongating, and the alar spines (which are possibly erectile) are 

 becoming conspicuous, tlie spinules along the anterior margin of the disk begin to 

 develop rapidly. When the claspers are fully elongated, these spinules, much 

 stouter than their fellows, form a band extending from the snout, to each angle of 

 the pectoral fins. 



The linear spines, when studied with reference to the gradual growth and 

 development of any one species are found to be subject to regular changes. So 

 much is this the case, that in diagnosing a species, writers have constantly 

 been compelled to make their statements capable of considerable elasticity of 

 interpretation. 



R. maculata must be described as possessing a central row of spines along the 

 back and tail, with one row or two rows on either side. In some cases the 

 central row is less prominent than the side row or rows ; in other cases the side 

 rows are only represented by a few isolated, but large spines. 



'■^ o "^ o *: o ^ \o + o + o + ''I 



[■*• o "*■ o + \o + o + O + 0/ 



r o "^ o '*' I lo + o + o + <'/ 



\^ o"^ o"^ o \ \o+o+o+W 



V o"^ o^ ol \o + o + o + o/ 



* ^ O o J \o + o + o + oj 



A B 



DiAG. 1 . — A represents a section of the tail of a very young specimen, two and a-half inches across, and B a section 

 from the tail of a specimen eight inches across. It will be noticed that in B the position of the rows 

 of signs has been reversed, the central row being in .<^ o and in B +. 



In R. circnlaris, at all stages, the tail is found to be possessed of many rows of 

 spines ; yet if a progressive series of examples be examined, a very instructive 

 system of alternation is discovered. 



In very small specimens of about 2^ inches across the wings, the whole surface 

 of the disk is more or less spinous, so as almost to resemble the condition seen in 

 R. radiata — a ray which does not occur in Irish waters, so far as present records 

 show us. The tail has a row of strong and prominent spines down the middle 

 line, but on the disk the difference between spines and spinules is not yet great. 

 On either side of this median row there is, at the root of the tail, a row of 

 insignificant spines. These cease on a level with the posterior margin of the 

 pelvic fin. On the outer side of each of these again comes a row of strong well- 

 marked spines, which run from the sides of the triangular patch in the centre of 

 the back to the end of the tail. Again, outside each of these rows there is a row 

 of feeble spines, which, about half-way along the tail, assume the extreme lateral 



