Holt and Calderwood — Report on the Rarer Fishes. 389 



larger examples.* Thus it would appear that the long-nosed skate resembles its 

 common ally in the spinulation formula, since in R. batis only a central row is 

 present in very young examples. The absence of median spines is a frequent 

 feature in old common skates, but we are not aware tliat any observer has 

 considered it of specific value, when dealing with that form. The apparent 

 anomaly that in such small species {e.g. R. maculata) as typically exhibit a 

 tri-linear arrangement of the caudal spines, it is the lateral and not the median 

 spines that are most often missing in old examples, is explained by the difference 

 in the history of the individual spines. In the small species the lateral spines, 

 which may, or may not, be present in the adult, are older than, or as old as, the 

 median spines, since they replace smaller spines, occupying the same position in 

 very young examples, at a period of the life history which presumably corresponds 

 to that which we have been dealing with in the case of the young long-nosed 

 skate. At about the same period the median spines of the Homelyn begin to be 

 replaced by the intercalation of a new series ; but in the large skates no such new 

 series is developed, and whatever median spines may be present in old examples 

 are only the remnants of the original series. It is easy to understand that the 

 renewal of the dermal armature of the young is a feature that would naturally be 

 lost in the evolution of a species which attains such a size as either R. batis, or 

 R. oxyrhynchus, the adults of which can have few enemies against which a prickly 

 tail would be an efficient defence. 



We have examined a mature male from Ireland ; but can say nothing as to the 

 spinulation of the tail, as that organ had, as usual, been cut off by the fishermen 

 for convenience of packing, before the specimen reached our hands. 



The dimensions are as follows : — 



Inches. 



Width of the disk 35 



Length of the snont, . . . . . . . • • Hi 



Length of the eye, 1^ 



Combined length of eye and spiracle, 2-|- 



Distance between the supra-orbital ridges, ..... 2|- 



Distance from tip of snout to centre of mouth, . . . . . 12 



Distance from tip of snout to ooracoid, . . . . . . 19 



Distance from tip of snout to anus, ....... 292- 



Distance between the inner margins of nostrils, ..... ^k 



Distance between the inner margins of either nostril and tip of snout, . 10 J. 



Length of the disk, .......... 30^ 



The claspers are fully elongated ; the vasa deferentia swollen ; but the testes 

 and the alimentary viscera are wanting. 



* It will be remembered that the most posterior of the lateral spines were wanting in the largest 

 examples, probably because these spines are the first to develop, and consequently the first to decay. 



