32 O. NOKDGAARD [1915 



p. 110) has examined a specimen of Ihis species tåken in the 

 Kristiania Fjord, near Drøhak, in August 1897. Total length was 

 98 mm. and probably newly emerged«. The largest embryonal 

 slages I have examined were 102 and 103 mm. The free young 

 stage mentioned b) 7 Collett was thus smaller than these embryos. 

 Il should be horne in mind, however, that the capsules vary a 

 good deal in size, the embryos probably also. Moreover, in the 

 embryonic stages there is a lail end which is doubtless east off 

 eilher shorlly before, or, more probably, immedialely after the 

 embryo emerges from the capsule, whereby the total length will 

 be reduced. Judging from my experience, therefore, vve mightwell 

 suppose that the specimen mentioned by Collett as measuring 

 93 mm. would at the close of the capsule stage have measured 

 abt. 110 mm. (93 - 17 mm.). 



The egg capsule of R. radiata and other Raja species have 

 been described, with illustrations, by Dr. H. C. Williamson 1 , 

 whose observations agree entirely with my own; the embryonal 

 development of R. radiata, however, has, as far as I am aware, 

 not hilherto been treated. There is, however, a study on the 

 development of Raja batis by Wyman 2 . I have not had access 

 lo Ihis work in the original, bul some extracts are given by 

 Lutken (Skildringer af Dyrelivet i Fortid og Nutid, Copenhagen, 

 1880) who also reproduces Wyman's figures. From these there 

 appears to be a very high degree of similarity between the 

 development in the two species of Raja in question. As far as 

 I can see, however, Wyman does not appear to have noticed 

 the free flap of the pectoral fin, which in my opinion is of 

 fundamental importance. The presence of this feature during 

 a part of the embryonal development reminds one of certain 

 Iransition forms between the sharks and the rays. In one such, 

 Raja squatina, where pectoral and ventral lie in the lateral plane 

 of the body, a free flap of the pectoral fin extends out beyond 

 the laterally adjacent gill slits. Lutken (1. c. p. 244) here cor- 

 rectly observed, that if »the pectoral fin had grown in to the 

 head, and the gill slits therefore been shifted over to the ventral 

 side, we should certainly have had to class this shark among 

 the rays«. Worthy of note is the fact that Raja radiata, at a 

 certain stage in its embryonal development, with the free flaps 

 of the pectoral fins, bears some resemblance to the above-men 



1 Fisheries. Scotland Sei. Invest. 1912 I Uuly 1913). 



2 Observations on the development of Raja batis, Memoirs of the 

 American Acad. of Arts and Sciences, new Ser. Vol. IX, part I, Cam- 

 bridge and Boston, 1867. 



