4 PROCEEDINGS OF THE NATIONAL MUSEUM vol. iis 



body and forms a keel on the peduncle and anterior part of the caudal 

 fin. I interpret the lower half of the divided ridge in the embryo to 

 be the same as the lowermost ridge in the adult, since posteriorly 

 the lower ridge forms the keel on the peduncle and caudal fin. 

 This means that, at a later date, a third ridge must appear above the 

 lower one in the embryo. Similar longitudinal ridges occur in some 

 members of the family Orectolobidae. The embryo also has a mid- 

 dorsal ridge which extends from the level of the first gill-opening to 

 the origin of the first dorsal fin and possibly is present between the 

 first and second dorsal fins. Adults have been described with and 

 without a middorsal ridge. 



Precaudal pits. — The embryo has a prominent upper precaudal pit, 

 with a notably wide, transverse front margin. There is also a small 

 but distinct lower precaudal pit. Adults are described as having the 

 upper pit but lacking the lower. 



Nostrils. — Reid (1957, p. 158) reported that each nostril in the em- 

 bryo is connected to the mouth by a distinct furrow — a character fre- 

 quently used to support the view that the whale shark is closely related 

 to, or belongs in, the family Orectolobidae. 



On the basis of an adult specimen, Barnard (1935, p. 649) disputed 

 this view. Without wishing to enter the controversy, I confirm Reid's 

 description that, in the embryo, there is no doubt that the nostril is 

 joined to the mouth by a naked or nearly naked furrow (pi. 4). How- 

 ever, in view of the close proximity of the nostril to the mouth, I won- 

 der if any significance can be placed upon this connection. Also, in 

 passing, I would mention that, in the embryo, the distance (in percent- 

 age of total length) from snout tip to outer nostril (0.6) is about half 

 that of snout tip to mouth (1.0). Bigelow and Schroeder (1948, p. 

 189) give the reverse of these figures for the adult they describe. 



Dermal denticles. — The dermal denticles of the embryo (pi. 3) 

 closely resemble those of the adult in having ovoid blades, each Avith 

 three posterior marginal teeth and a strong median longitudinal keel. 

 Some denticles from the lower longitudinal dermal trunk ridge, how- 

 ever, are distinctly larger and are arranged in longitudinal pairs, with 

 the anterior denticle overlapping the one posterior to it. These pairs 

 are clearly visible not only because of their larger size, but also because 

 of their darker pigmentation. The posterior denticle of each pair is 

 similar in shape to the surrounding body denticles, but usually it has a 

 broader topped longitudinal ridge. The anterior denticle is of the 

 same size, but it is more nearly oval in shape, with only a median pos- 

 terior tooth; its longitudinal ridge is broadly expanded and round 

 topped, and usually it bears several minor ridges which converge 

 posteriorly to form a single ridge. 



