328 THE PROCEEDINGS OF THE LINNEAN SOCIETY 



convenient, if somewhat primitive method. This consisted in 

 the preparation of outlines of the object laid on paper ; the 

 natural-size sketches, thus obtained, were then reduced by the 

 orthodox method. To the figures prepared from photographs, 

 the respective scales* are annexed, in order to render possible a 

 rough estimate of the amount of reduction or enlargement, since 

 the method of preparing photographs to scale is yet unknown to 

 me. 



EXPLANATION OF THE PLATES. 



Lettering Followed Throughout all the Figures (With the 

 Exception of Plate 24). 



a — Superior oral fold. 



h — Inferior oral fold. 



n — External orifice of the nasal groove. 



n' — C Border of the internal fold of the nasal groove. 



7i!' — Orifice of the nasal groove in the oral cavity. 



s'p — Spiracle. 



PLATES 22 AND 23. 



(Heterodontus Phillipi, Bl.) 



Figs. 1, 2 (pi. 22) 5, 6, 7 (pi. 23).— Young H. Phillipi, 225 

 mm. in length drawn from a fresh specimen. 



Fig. 1. — Posterior view of the same. The young animal 

 shewed the peculiar marking, somewhat different from that of 

 the adult, very distinctly, as the brownish -black stripes stood out 

 very markedly on the very transparent skin of the young at this 

 stage. 



* — Transverse black bar which passes over the head from eye 

 to eye, and loses itself on the cheeks. ** — Characteristic mark 

 between the dorsal and ventral fins. 



Besides the very remarkable marking, the rounded form of the 

 head and the proportionally large tail are peculiar to this stage. 



* N.B. — The scale can only be relied on for a certain part of the object (the part on the 

 same plane with it), and must, therefore, be used with caution. 



